˘ˇ ˆ˙ - US EPA · PDF fileNOX Control Technologies for the Cement Industry FINAL...

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EPA-457/R-00-002

September 2000

NOX Control Technologies for the Cement Industry

FINAL REPORT

EPA Contract No. 68-D98-026

Work Assignment No. 2-28

EC/R Project No. ISD-228

Prepared for:

Mr. David Sanders

Ozone Policy and Strategies Group

Air Quality Strategies and Standards Division, MD-15

Office of Air Quality Planning and Standards

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

Prepared by:

Rebecca Battye, Stephanie Walsh, Judy Lee-Greco

EC/R Incorporated

1129 Weaver Dairy Road, Suite AA-1

Chapel Hill, NC 27514

September 19, 2000

i

TABLE OF CONTENTS

1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 PURPOSE OF THIS DOCUMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.3 ORGANIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.4 REFERENCE FOR CHAPTER 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2.0 SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.1 UNCONTROLLED NOX EMISSIONS FROM CEMENT KILNS . . . . . . . . . . . 2

2.2 NOX CONTROL TECHNOLOGY FOR CEMENT KILNS . . . . . . . . . . . . . . . . . 4

2.2.1 Process Control Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2.2 Combustion Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.3 NOX Removal Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2.4 NOX Control Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3 CONTROL COSTS AND COST EFFECTIVENESS . . . . . . . . . . . . . . . . . . . . . . 8

2.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.0 INDUSTRY DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 TYPES OF CEMENT PRODUCED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3 INDUSTRY CHARACTERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3.1 Description of the Cement Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3.2 Overview of Cement Manufacturing Process . . . . . . . . . . . . . . . . . . . . . 21

3.3.3 Raw Materials and Kiln Feed Preparation . . . . . . . . . . . . . . . . . . . . . . . . 21

3.3.4 Pyroprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.3.4.1 Wet Process Kilns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.3.4.2 Dry Process Kilns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.3.4.3 Suspension Preheaters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.3.4.4 Precalciner Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.3.5 Finish Grinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.6 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.7 Emission Control Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.0 UNCONTROLLED NOX EMISSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.1 MECHANISMS OF NOX FORMATION IN CEMENT MANUFACTURING . . . 29

4.1.1 Thermal NOX Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.1.2 Fuel NOX Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.1.3 Feed NOX Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

ii

TABLE OF CONTENTS (continued)

4.2 FACTORS AFFECTING NOX EMISSIONS IN CEMENT MANUFACTURING . 32

4.2.1 NOX Formation in the Kiln Burning Zone . . . . . . . . . . . . . . . . . . . . . . . . 33

4.2.2 NOX Formation in Secondary Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.2.2.1 Suspension Preheater (SP) Kilns with Riser Duct Firing . . . . . . 35

4.2.2.2 Precalcining Kiln Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.2.3 Energy Efficiency of the Cement-Making Process . . . . . . . . . . . . . . . . . 36

4.3 AVAILABLE DATA FOR UNCONTROLLED NOX EMISSIONS FROM CEMENT

MANUFACTURING FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.0 NOX CONTROL TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

5.1 PROCESS CONTROL MODIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

5.1.1 Combustion Zone Control of Temperature and Excess Air . . . . . . . . . . . . 54

5.1.2 Feed Mix Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.1.2.1 Reduction of Alkali Content of Raw Feed . . . . . . . . . . . . . . . . . 55

5.1.2.2 CemStar Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.1.3 Kiln Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.1.4 Increasing Thermal Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5.2 COMBUSTION MODIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5.2.1 Staged Combustion of Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5.2.1.1 Flue Gas Recirculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

5.2.1.2 Low-NOX Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

5.2.2 Staged Combustion of Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

5.2.2.1 Preheater/Precalciner and Tire Derived Fuel . . . . . . . . . . . . . . . 62

5.2.2.2 Low-NOX Precalciners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

5.2.2.3 Mid-Kiln Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

5.3 NOX REMOVAL CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

5.3.1 Selective Catalytic Reduction (SCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

5.3.2 Selective Noncatalytic Reduction (SNCR) . . . . . . . . . . . . . . . . . . . . . . . . 70

5.3.2.1 Biosolids Injection (BSI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

5.3.2.2 NOXOUT® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

5.4 SUMMARY OF EUROPEAN EXPERIENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

5.5 SUMMARY OF APPLICABLE NOX CONTROL TECHNOLOGIES . . . . . . . . . . 76

5.6 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

6.0 COSTS OF NOX CONTROL TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

6.1 COST CALCULATION METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

6.1.1 Model Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

6.1.2 Capital Cost Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

iii

TABLE OF CONTENTS (continued)

6.1.3 Annual Operating Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

6.1.3.1 Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

6.1.3.2 Operating and Supervising Labor . . . . . . . . . . . . . . . . . . . . . . . . 87

6.1.3.3 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.1.3.4 Overhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.1.3.5 Property Taxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.1.3.6 Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.1.3.7 Administrative Charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.1.3.8 Capital Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.2 COSTS OF NOX CONTROL APPROACHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.2.1 Process Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

6.2.1.1 Combustion Zone Control of Temperature and Excess Air . . . . 89

6.2.1.2 CemStar Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

6.2.2 Combustion Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

6.2.2.1 Low NOX Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

6.2.2.2 Mid-Kiln Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

6.2.3 NOX Removal Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

6.2.3.1 Biosolids Injection Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

6.2.3.2 NOXOUT®. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

6.2.3.3 Selective Catalytic Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 101

6.3 COST EFFECTIVENESS OF NOX CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . 102

6.3.1 CemStar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

6.3.2 Low NOX Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

6.3.3 Mid-Kiln Firing of Tires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

6.3.4 Preheater/Precalciner Tire Derived Fuel . . . . . . . . . . . . . . . . . . . . . . . . . 105

6.3.5 Biosolids Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.3.6 Selective Noncatalytic Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.3.7 Selective Catalytic Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.3.8 Summary of Cost Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

6.4 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

iv

LIST OF TABLES

Table 2-1. Summary of Updated Uncontrolled NOX Emissions Data and the

Corresponding 1994 Act Document Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Table 2-2. Comparison of 1994 Act Document and Current NOX Control Technology

Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 2-3. Summary of Cost Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Table 3-1. Basic Clinker Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 3-2. United States Cement Company Capacities in 1998 . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 3-3. United States 1998 Clinker Capacities by State . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 4-1. Calculated Equilibrium Concentrations (in ppm) of NO and NO2

in Air and Flue Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Table 4-2. NOX Emissions Data Used to Develop 1994 Act Document . . . . . . . . . . . . . . . . . . 38

Table 4-3. Summary of Additional NOX Emission Data for Different Kiln Types . . . . . . . . . . 48

Table 4-4. Comparison of Emission Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Table 4-5. NOX Emission Factors for Different Kiln Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Table 5-1. Results of Short-term Cemstar Tests on a Preheater/precalciner Kiln . . . . . . . . . . . 56

Table 5-2. Results of Cemstar Tests on a Wet Kiln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Table 5-3. NOX Emissions from a Precalciner Equipped with a Low-NOX Burner . . . . . . . . . . 60

Table 5-4. NOX Emissions Before and after Installation of Pyro-jet Low-NOX Burners . . . . . . 61

Table 5-5. NOX Emissions with 3 Channel and Rotaflam® Low-NOX Burners . . . . . . . . . . . . . 61

Table 5-6. Emissions Before and after Installation of a Rotaflam® Burner on a Wet Kiln . . . . 62

Table 5-7. Emissions from Kilns with Mid-kiln Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Table 5-8. Emission Reductions from Two Kilns Using NOXOUT® . . . . . . . . . . . . . . . . . . . . . 74

Table 5-9. NOX Control Techniques Summary from European Best Available Techniques Report75

Table 5-10. NOX Control Techniques and Applicable Types of Cement Kilns . . . . . . . . . . . . . 76

Table 5-11. Comparison of 1994 Act NOX Emissions Reductions with Newly Available

Emissions Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

v

LIST OF TABLES (continued)

Table 6-1. Cement Kiln Model Plants for Cost Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Table 6-2. Capital Investment Components for Emission Control Device Cost Evaluation . . . 86

Table 6-3. Annualized Cost Elements and Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Table 6-4. Basis for Cost Analysis of Cemstar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Table 6-5. Capital Costs for Retrofit Low-NOX Burners in an Existing Indirect-fired Kiln . . . 93

Table 6-6. Annualized Costs for Retrofit Low-NOX Burners in an Existing Indirect-fired Kiln 94

Table 6-7. Capital Costs for Retrofit Low-NOX Burners in an Existing Direct-fired Kiln . . . . . 96

Table 6-8. Annualized Costs for Retrofit Low-NOX Burners in an Existing Direct-fired Kiln . 97

Table 6-9. Capital Costs for Mid-kiln Firing Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Table 6-10. Annualized Costs for Mid-kiln Firing Conversion . . . . . . . . . . . . . . . . . . . . . . . . . 99

Table 6-11. Basis for Cost Analysis of Biosolids Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Table 6-12. Basis for Cost Analysis of NOXOUT® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Table 6-13. Capital Costs for SCR Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Table 6-14. Annualized Costs for SCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Table 6-15. Cost Effectiveness of Retrofit Low-NOX Burners in an Existing Indirect-fired

Kiln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Table 6-16. Cost Effectiveness of Retrofit Low-NOX Burners in an Existing Direct-fired

Kiln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Table 6-17. Cost Effectiveness of Mid-kiln Firing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Table 6-18. Cost Effectiveness of SCR Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Table 6-19. Summary of Cost Effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

vi

LIST OF FIGURES

Figure 3-1. Annual clinker production. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 3-2. United States and Canadian Portland Cement Locations

(December 31, 1998) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 3-3. Steps in the manufacture of portland cement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 3-4. Preheater/precalciner cement kiln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 4-1. Theoretical equilibrium concentrations of NO in gas from combustion

sustained in air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 5-1. Schematic of low-NOX burner. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Figure 5-2. Schematic of preheater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Figure 5-3. Schematic of precalciner. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Figure 5-4. Reduction of NOX emissions from precalcining kiln system by fuel injection

in the rotary kiln gas outlet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Figure 5-5. Schematic of mid-kiln firing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Figure 5-6. Schematic of fuel injection in kiln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Figure 5-7. Application of SNCR in preheater kiln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

1

1. U.S. Environmental Protection Agency. Alternative Control Techniques Document - NOX

Emissions from Cement Manufacturing. EPA-453/R-94-004. Research Triangle Park,

NC. March 1994.

1.0 INTRODUCTION

1.1 PURPOSE OF THIS DOCUMENT

The purpose of this document is to update the information in the document Alternative

Control Techniques Document - NOX Emissions from Cement Manufacturing (the 1994 ACT

document).1 This update incorporates comments received on the 1994 ACT document and

provides more recent data on emission control technologies and their costs.

This report examines uncontrolled emissions from four kiln types (wet, long dry,

preheater, precalciner). The report focuses on the current use, effectiveness, and cost of several

control technologies applicable to all or some kiln types, including CemStar, low-NOX burners,

mid-kiln firing, and selective noncatalytic reduction via biosolids injection and NOXOUT®

technology.

1.2 METHODS

Data were collected for this report primarily through site visits at cement kiln facilities;

contacts with control technology vendors, portland cement industry representatives, and state

regulatory agencies; and a literature search. Additional information was obtained through

seeking out useful sites on the internet.

1.3 ORGANIZATION

Chapter 2 presents a summary of the findings of this study. Chapter 3 provides a

description of the portland cement industry. Chapter 4 examines uncontrolled NOX emissions.

Chapter 5 presents an update on selected NOX control technologies. Chapter 6 presents an

update on control costs and cost effectiveness.

1.4 REFERENCE FOR CHAPTER 1

2

2.0 SUMMARY

This report addresses nitrogen oxides (NOX) emissions from portland cement kilns and

the current use, effectiveness, and cost of applicable control technologies. This chapter presents

a summary of updated information on uncontrolled NOX emissions from kilns and the

applicability, effectiveness, and costs of NOX control technologies. Information that is

summarized in this chapter is presented in greater depth in subsequent chapters. Section 2.1

includes a summary of current uncontrolled NOX emissions data from the four kiln types.

Section 2.2 summarizes NOX control technology emissions data. Section 2.3 presents a summary

of updated control costs and cost effectiveness for these control technologies.

2.1 UNCONTROLLED NOX EMISSIONS FROM CEMENT KILNS

In cement manufacturing, conditions favorable for formation of NOX are reached

routinely because of high process temperatures. Essentially all NOX emissions associated with

cement manufacturing are generated in cement kilns.

In cement kilns, NOX emissions are formed during fuel combustion by two primary

mechanisms:

• Oxidation of molecular nitrogen present in the combustion air, which is termed

“thermal NOX” formation, and

• Oxidation of nitrogen compounds present in the fuel, which is termed “fuel NOX”

formation.

Often the raw material feed to the kiln contains a significant amount of nitrogen compounds

which may lead to feed NOX formation similar to fuel NOX formation. Because of the high

temperatures involved in the burning or clinker formation step, thermal NOX formation provides

the dominant mechanism for NOX formation in cement manufacturing.

There are four different types of cement kilns used in the industry: wet kilns, long dry

kilns, kilns with a preheater, and kilns with a preheater/precalciner. All cement kiln systems

contain a rotary kiln. The wet, long dry, and most preheater kilns have only one fuel combustion

zone; whereas, the newer preheater/precalciner kilns and preheater kilns with a riser duct have

two fuel combustion zones. Some precalciner kilns have a third combustion zone. Since the

typical temperatures in the combustion zones are different, the factors affecting NOX formation

are also somewhat different in the different kiln types. In the primary combustion zone at the hot

end of a kiln, the high temperatures lead predominantly to thermal NOX formation; whereas, in

secondary combustion zones lower gas-phase temperatures suppress thermal NOX formation.

In addition to the specific NOX formation mechanisms, the energy efficiency of the

cement making process is also important as it determines the amount of heat input needed to

3

produce a unit quantity of cement. A high thermal efficiency would lead to less consumption of

heat and fuel, and should produce lower NOX emissions per ton of clinker, the product of the

rotary kiln.

EC/R obtained emissions data for cement kilns from state regulatory agencies in eight of

the top ten states in terms of clinker capacity: California, Florida, Indiana, Michigan, Missouri,

New York, Pennsylvania, and Texas. Table 2-1 presents a summary of the recent state emissions

data alongside a summary of the estimates used in the 1994 ACT document and the current

edition of AP-42.

TABLE 2-1. SUMMARY OF UPDATED UNCONTROLLED NOX EMISSIONS DATA

AND THE CORRESPONDING 1994 ACT DOCUMENT ESTIMATES

1994 ACT Document1 AP-42 2 Recent State Data3

Cement kiln type

Average

(lb/ton of

clinker)

Range

(lb/ton of

clinker)

(lb/ton of

clinker)

Average rate

(lb/ton of

clinker)

Range of rates

(lb/ton of

clinker)

Wet kiln 9.7 3.6 to 19.5 7.4 6.2 1.9 - 13.4

Long dry kiln 8.6 6.1 to 10.5 6.0 4.5 2.5 - 7.1

Preheater kiln 5.9 2.5 to 11.7 4.8 1.7 0.4 - 3.7

Precalciner kiln 3.8 0.9 to 7.0 4.2 2.9 1.1 - 5.6

There is substantial spread in the reported NOX emissions with significant overlap for

different kiln types. The four different cement kiln types, however, do appear to have different

levels of NOX emissions and different characteristics influencing NOX formation. Information

used to calculate NOX uncontrolled emission rates come from air emission tests at various

cement manufacturing facilities in the United States. Twenty-two tests were used to calculate the

AP-42 NOX emission factors and all of the tests are over ten years old. In addition, the majority

of these are short-term emissions tests, which do not capture the inherent variability of kiln NOX

emissions. As a result, the AP-42 NOX emission factors have a quality rating of “D” (relatively

low quality - limited data, or highly variable). When one reviews the original data summarized

in the 1994 ACT document, it is clear that the average emission rates are not unduly influenced

by outliers as evidenced by the fact that the average for each kiln type is nearly in the middle of

the range. Because the data used in the calculation of the 1994 ACT document NOX emission

rates are newer, these average emission rates may be more representative of modern kilns than

the factors presented in AP-42.4

Seven of the states that were contacted reported emissions in tons NOX/year. Six of these

states did not report production values, so kiln capacities5 were used to determine emission rates.

The kilns were assumed to operate for an average of 8,000 hours/year at maximum production

capacity. The resulting average emission rates are generally lower than the average emission

4

rates calculated in the 1994 ACT document or presented in AP-42. The lower numbers are

probably a result of using kiln capacities rather than actual kiln production values. Because of

the uncertainty surrounding the production values for the state data and because the AP-42 data

have a “D” rating, the 1994 ACT document values for uncontrolled NOX emissions from cement

kilns are used in this document. However, it should be noted that the ranges in emissions and the

average values for all three data sources generally support one another. Chapter 4 contains more

detailed information on the uncontrolled NOX emission values.

2.2 NOX CONTROL TECHNOLOGY FOR CEMENT KILNS

NOX control approaches applicable to the cement industry may be grouped in three

categories: process modifications, where the emphasis is on increased energy efficiency and

productivity; combustion control approaches, where the emphasis is on reducing NOX formation;

and NOX reduction controls, which remove the NOX formed in the combustion process.

2.2.1 Process Control Modifications

Process modifications are usually done to reduce heat consumption, to improve clinker

quality, and to increase the lifetime of the equipment (such as the refractory lining) by stabilizing

process parameters. Process modifications are applicable to all kilns and can include many

elements, such as instruction and training of the kiln operators, homogenizing raw material,

ensuring uniform coal dosing, improving the cooler’s operation, and installing new equipment.

Process modifications improve fuel efficiency, reduce operating costs, increase capacity and kiln

operational stability. Since NOX formation is directly related to the amount of energy consumed

in cement-making, improving fuel efficiency and productivity will reduce NOX emissions.

Continuous monitoring of oxygen and carbon monoxide emissions in the cement kiln

exhaust gases indicates the amount of excess air. At a given excess air level, NOX emissions

increase as the temperature of the combustion zone increases. A typical kiln combustion zone

solids temperature range is about 1430 to 1540 C (2600 to 2800 F) for completion of

clinkering reactions and to maintain the quality of the cement produced.6 The corresponding gas-

phase temperature is usually greater than 1700 C (3100 F).7 Maintaining the combustion zone

temperature at the minimum necessary value would minimize both the process energy

requirement and the NOX emissions.

Along with the appropriate temperature, it is also necessary to maintain an oxidizing

atmosphere in the clinker burning zone to ensure the quality of the clinker produced. Although a

kiln could be operated with as little as 0.5 percent oxygen in the exhaust, kiln operators typically

strive for an oxygen level of 1 to 2 percent to guarantee the desired oxidizing conditions in the

clinker burning zone. An experimental test on a cement kiln showed that by reducing excess air

from 10 to 5 percent (i.e., reducing exhaust oxygen levels from 2 to 1 percent), NOX emissions

per unit time can be reduced by approximately 15 percent.8,9

5

With state-of-the-art continuous emissions monitoring systems (CEMS) and feedback

control, excess air can be accurately controlled to maintain a level that promotes optimum

combustion and burning conditions in addition to lowering NOX emissions. Reducing excess air

levels also results in increased productivity per unit of energy consumed and thus results in an

indirect reduction of NOX emissions per unit of clinker product.

Process modifications can be highly site specific and data from one site cannot be directly

translated to other sites. Quite often a number of process modifications and combustion control

measures are implemented simultaneously. Process modifications can reduce NOX emissions in

cement kilns without any specific NOX control equipment. Some plants rely on process

monitoring and control and process modifications as a means to maintain NOX emissions within

their allowable limits. Although process controls will reduce NOX emissions in poorly operated

kilns, for the purposes of this document, such approaches are considered necessary for proper

kiln operation and are not specifically considered as NOX control techniques, except as noted

below for CemStar.

One process modification that can be quantified is the CemStar process, which can reduce

NOX emissions at any type of kiln by the addition of a small amount of steel slag to the raw kiln

feed. Steel slag has a low melting temperature and is chemically very similar to clinker. Since

many of the chemical reactions required to convert steel slag to clinker have already taken place

in a steel furnace, the fuel needed to convert steel slag into clinker is low. The decreased need

for limestone calcination per unit product and improved thermal efficiency of the process both

contribute to reduced thermal NOX and carbon dioxide emissions.10 CemStar is currently being

used or is in the process of being incorporated at 11 cement facilities in the United States.

CemStar requires little extra equipment and the addition of steel slag to the feed mix can result in

a reduction or elimination of the need for some mineral sources, such as shale or clay. This

process can decrease NOX emissions by 30% and can also increase production by 15 percent.10

2.2.2 Combustion Modifications

Combustion modifications are an efficient way to reduce the formation of thermal NOX.

The combustion modifications discussed in this report focus on staging the combustion to

minimize the amount of combustion that must occur at the maximum temperatures. This can be

accomplished by modifying the way oxygen or fuel is provided for combustion.

Low-NOX burner systems are available for all kiln types and rely on the staged

combustion of air. Technical literature and industry publications report NOX reduction rates of

23 to 47 percent with the installation of low-NOX burners, depending on the baseline emissions,

type of kiln, type of low-NOX burner, and operating conditions.11,12,13,14,15 In January 2000, the

Portland Cement Association (PCA) and American Portland Cement Alliance (APCA) provided

results of a survey of cement facilities where the respondents indicated 14% of the operating U.S.

kilns have already installed a low-NOX burner (81% of the facilities representing 81% of the

operating U.S. kilns responded to the survey).16,17

6

Staged combustion of fuel includes the use of preheaters/precalciners and mid-kiln firing.

Mid-kiln firing of fuels is currently installed in 21 U.S. wet and long dry cement kilns, and whole

tires are most frequently used for the mid-kiln fuel. Technical literature, industry publications,

and state emissions data for several kilns that have used or tested mid-kiln firing demonstrate

NOX reductions ranging from 28 to over 50 percent.18,19,20,21,22,23,24 Use of tire derived

supplemental fuel at a preheater/precalciner has been shown to decrease NOX emissions by 30-40

percent.25

2.2.3 NOX Removal Control

NOX removal controls destroy NOX that is formed in the combustion process. Selective

catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) are two types of NOX

removal controls. Biosolids injection technology is not technically SNCR, but the chemistry and

the principles of its operation are similar. For this reason it is discussed with the other NOX

removal controls.

SCR uses ammonia in the presence of a catalyst to selectively reduce NOX emissions

from exhaust gases. SCR technology has not been used on any cement kilns in the United States,

although pilot plant trials and feasibility studies have been conducted in Europe.

SNCR relies on the reduction of NOX in exhaust gases by ammonia or urea without using

any catalyst and can achieve NOX emission reductions of 30 to 70 percent. This approach avoids

the problems related to catalyst fouling, as in SCR technology, but requires injection of the

reagents in the kiln at a temperature between 870 to 1090 C (1600 to 2000 F). At these

temperatures urea decomposes to produce ammonia which is responsible for NOX reduction.

Because of the temperature constraint, SNCR technology is only applicable to preheater and

precalciner kilns. In principle, any of a number of nitrogen compounds may be used, e.g.,

cyanuric acid, pyridine, and ammonium acetate. However, for reasons of cost, safety, simplicity,

and by-product formation, ammonia and urea have been used in most of the SNCR applications.

There have been two SNCR demonstration at full size kilns in the United States using the

NOXOUT® process.26,27 SNCR is currently operating on numerous kilns in Europe.28

Biosolids injection technology is being used in one kiln in Southern California.29,30 At

this facility, the biosolids (dewatered sewage sludge) are injected into the mixing chamber where

the flue gas streams leaving the kiln and precalciner mix. The mixing chamber offers the

benefits of good residence time in the appropriate temperature window and high mixing

effectiveness. Biosolids injection is achieving a 50 percent NOX emission reduction at this

facility.

2.2.4 NOX Control Efficiencies

An assortment of industry data, literature, and professional publications, as well as some

of the state data described above, was used to develop an estimate of emissions from cement

7

kilns using NOX control technologies. Table 2-2 presents a summary of updated control

technology emission rates alongside the emission estimates used in the 1994 ACT document.

The new emissions rates are all within or very close to the ranges established in the 1994 ACT

document. CemStar, a relatively new process that involves adding steel slag to the feed mix in a

long kiln, was not discussed in the 1994 ACT document. Emission rate reductions from the use

of CemStar averaged 33 percent. New data on low-NOX burners and mid-kiln firing tend to

support the information presented in the 1994 ACT document. Both of these technologies have

become more commonplace in controlling NOX emissions from cement kilns and improved

performance using mid-kiln firing technology has been obtained. Data were also obtained on

two SNCR technologies, biosolids injection and NOXOUT®. These technologies showed average

emission reductions of 50 and 40 percent, respectively. Additional information on SCR was not

obtained during the development of this report. Chapter 5 contains a more detailed discussion of

the NOX control technologies.

TABLE 2-2. COMPARISON OF 1994 ACT DOCUMENT AND CURRENT

NOX CONTROL TECHNOLOGY PERFORMANCE

1994 ACT Updated Emissions Data3

Possible

NOX

Emission

Reduction

(%)

Average

Emission

Reduction

(%)

Range of

Emission

Reductions

(%)

Average

Emission

Rate

(lb NOX/ton

of clinker)

Range of

Emission

Rates Found

(lb NOX/ton

of clinker)

Process Control

Modifications

<25

CemStar n/a 33 23 to 40 6.0 3.2 to 11.2

Indirect firing

with a low-NOX

burner

20 to 30 27 4 to 47 9.0a 9.0a

MKF

(wet kilns only)

20 to 40 41 28 to 59 n/a n/a

MKF

(dry kilns only)

20 to 40 33 11 to 55 3.9 2.0 to 10

TDF in a

precalcinerb

not

applicable

35 30 to 40 2.4b 2.4b

SNCR 30 to 70 BSI 50 NA 1.2b 1.2b

NOX-

OUT

40 10 to 50 NA NA

n/a - not applicablea Only one facility reported emissions in lb NOX/ton of clinker. The other data were reported in

percent.

8

b One facility in southern California provided emission reduction data for both biosolids injection

technology and firing tire derived fuel in a precalciner.

2.3 CONTROL COSTS AND COST EFFECTIVENESS

Capital and annualized operating costs as well as cost effectiveness were determined for

technologies for which detailed costs could be developed. Costs for low-NOX burners and mid-

kiln firing were developed for applicable model plants. Since there are limited cost data

available for installations of CemStar and biosolids injection, and no U.S. installations of SNCR,

the capital and annualized costs for these technologies were not developed for model plants for

purposes of this report. Costs for SCR were developed in the 1994 ACT document and are

presented again in this report. The SCR costs have not been updated or revised. All of the

capital and annualized operating costs developed for this report are based on information

provided by vendors, actual installations, and guidelines provided by the U.S. Environmental

Protection Agency/Office of Air Quality Planning and Standards (EPA/OAQPS) Control Cost

Manual.

The cost of a commercially available kiln process control system, based on existing

installations, is approximately $750,000. The resulting savings due to reduced energy and fuel

requirements and increased refractory life were estimated to be about $1.37/ton of clinker. Thus,

for a kiln producing 300,000 tons/year of clinker, the reduced cost of producing cement is

expected to recover process control installation costs in less than 2 years.

Costs for CemStar were estimated for a long wet kiln. Approximate capital investment in

1997 dollars was estimated at $1,176,000 and annualized costs estimated to be $220,000. Cost

savings associated with CemStar due to the resulting production increase are estimated to be

approximately $63 per ton times the increase in production, which is usually 5 to 10 percent.

The cost of CemStar could not be estimated on a variety of kilns because the amount of steel slag

added is completely dependent on plant-specific variables.

Biosolids injection has been installed on one kiln. The total capital investment costs for

this kiln were $1.2 million with an annual operating cost of ($322,000) per year (which includes

tipping fees for the biosolids of $5/ton). Costs for NOXOUT® technology were obtained from the

equipment vendor for two preheater/precalciner kilns. Total capital investment were $1.06

million and $1.2 million. The annualized costs for these kilns are $560,000 and $2,000,000 per

year.

Cost analysis was performed for low-NOX burners and mid-kiln firing on up to eight

different model kilns. Models 1 and 2 were wet kilns with 30 and 50 tons of clinker per hour

(ton/hour) respective capacities, models 3 and 4 were long dry kilns with 25 and 40 ton/hour

respective capacities, models 5 and 6 were preheater kilns with 40 and 70 ton/hour respective

capacities, and models 7 and 8 were precalciner kilns with 100 and 150 ton/hour respective

capacities. The results of the cost analysis in 1997 dollars are summarized in Chapter 6.

9



NC. March 1994.

2. U.S. Environmental Protection Agency. Compilation of Air Pollutant Emission Factors.

AP-42. Fifth Edition. Volume I - Stationary Point and Area Sources. Research Triangle

Park, NC. January 1995. pp. 11.6-1 - 11.6-26.

Cost effectiveness was also estimated for each technology. A summary of the results is

presented in Table 2-3. Greater detail on the cost analysis and cost effectiveness estimates is

presented in Chapter 6.

TABLE 2-3. SUMMARY OF COST EFFECTIVENESS

(1997 Dollars/ton NOX Reduced)

Technology Range of Annual

Cost Effectiveness

Average Annual

Cost Effectiveness

Average Ozone

Season Cost

Effectiveness

CemStar n/a 550 1,100

Low-NOX

Burners

Indirect-

Fired Kilns

300 to 620 440 1,060

Direct-Fired

Kilns

760 to 1200 940 2,260

Mid-Kiln Firing (460) to 730 55 130

Tire Derived Fuel at a

Precalcinera

(1,900)b (1,900)b (4,500)b

Biosolids Injection n/a (310)b (740)b

NOXOUT® 1,000 to 2,500 1,750 2,160

N/A - not applicable

( ) - indicates a negative costa The purchased equipment and total capital investment costs for a tire derived fuel installation

on a precalciner are very similar to mid-kiln firing.b Represents a single installation.

2.4 REFERENCES

10

3. Memo from Battye, R., and S. Walsh, EC/R Incorporated, Chapel Hill, NC to D. Sanders,

U.S. EPA, RTP, NC. Derivation and data supporting development of cement plant NOX

emission rates. September 5, 2000.

4. Strietman, F.L, T.B. Carter, and G.J. Hawkins. Regulation and Control of NOX Emission

from the Portland Cement Industry. Presented at the 1999 IEEE Gulf Coast Cement

Industry Conference. Charleston, SC. September 30 and October 1, 1999.

5. Portland Cement Association. U.S. and Canadian Portland Cement Industry: Plant

Information Summary. Skokie, IL. December 31, 1998. 214 pp.

6. Helmuth, R.A., F.M. Miller, T.R. O'Connor, and N.R. Greening. Kirk-Othmer

Encyclopedia of Chemical Technology. Vol. 5. Third Edition. New York, NY. John

Wiley & Sons, Inc. 1979. pp. 163-193.

7. Yee, G.M. Suggested Control Measure for the Control of Emissions of Oxides of

Nitrogen from Cement Kilns. Presented to the State of California, Air Resources Board

for Discussion on October 21, 1981.

8. Miller, F.M. Oxides of Nitrogen. GTC Presentation, Kansas City, MO, September 20,

1977.

9. Hansen, E.R., “The Use of Carbon Monoxide and Other Gases for Process Control,” 27th

IEEE Cement Industry Technical Conference Proceedings, May 1985.

10. Andover Technology Partners. NOX Reduction from Cement Kilns Using the CemStar

Process, Evaluation of CemStar Technology - Final Report to Texas Industries. Dallas,

Texas. April 18, 2000.

11. Thomsen, K., L.S. Jensen, and F. Schomburg. FLS-Fuller ILC-lowNOx calciner

commissioning and operation at Lone Star St. Cruz in California. ZKG International.

October 1998. pp. 542 - 550.

12. Steinbiß, V.E., C. Bauer, and W. Breidenstein. Current state of development of the

PYRO-JET® burner. VDZ Kongress. 1993.

13. Letter and attachments from M.H. Vaccaro, Pillard Combustion Equipment and Control

Systems, to G.J. Hawkins, Portland Cement Association, re: Low NOX Rotaflam®

burner, dated January 20, 1999.

14. PSM International, “Response to USEPA Comments, 13 September 1995, on the

proposed alternative NOX RACT for a portland cement manufacturing plant located in

Thomaston, Maine and owned by Dragon Products Company,” Jan 31, 1996.

11

15. Renfrew, S, Process Engineer, RMC Lonestar. Calciner modification highly effective in

meeting Northern California Plant’s alkali reduction and emission control requirements.

no date.

16. Email transmission from Hawkins, G., PCA, Skokie, IL to B. Neuffer, U.S. EPA. Results

of PCA Survey - Preliminary NOX Control Technology Questionnaire. January 2000.

17. Letter from R. Battye and S. Edgerton, EC/R Incorporated, Chapel Hill, NC, to B.

Neuffer, USEPA, RTP, NC. Summary of February 4, 2000 conference call on PCA

Survey - Preliminary NOX Control Technology Questionnaire. February 11, 2000.

18. Walquist, C., Cadence Environmental Energy. “Cadence system leads to fall in NOX

emissions,” World Cement, Dec 1997, pp. 26, 27.

19. Cadence Environmental Energy and Ash Grove Cement. “Mid-Kiln Fuel Entry

Benefits,” section 3 of the report, Emission, Reduction, Technology: Resource

Conservation & Recovery. (no date).

20. Letter from Edgerton, S. and T. Stobert, EC/R Inc., to Bill Neuffer, EPA, Feb 8, 2000.

Minutes from Dec 16, 1999 meeting with representatives from EPA and Cadence.

21. Texas Natural Resources Conservation Commission. A list of permitted NOX levels for

cement plants in the state, CEMS data as reported by the facilities for 1994 - 1999, and

information on the control technology in use at each facility.

22. May, M. and L. Walters, Jr. "Low NOX & Tire-derived Fuel for the Reduction of NOX

from the Portland Cement Manufacturing Process." Cement Americas, August 1999, pp.

10-1.

23. Letter and attachments from Bramble, Kim, Cadence, to Bill Neuffer, USEPA, re: NOX

Emission Reducing Technology, dated Feb 14, 2000.

24. Radian Corporation, "MDE Air Permit Test Report for Lehigh Portland Cement

Company, Union Bridge, Maryland Facility," January 1996.

25. Shumway, D.C. “Tire Derived Fuel at Mitsubishi Cement Corporation.” Received

during December 2, 1999 visit to Mitsubishi.

26. Sun, et. al. Reduction of NOX Emissions from Cement Kiln/ Calciner through the Use of

the NOXOUT Process. Presented at the International Specialty Conference on Waste

Combustion in Boilers and Industrial Furnaces. Kansas City, MO. April 1994.

27. Interoffice Correspondence from McAnany, L. to H. Knopfel, H, LaFarge Corporation.

October 26, 1998. re: Fuel Tech NOXOUT Testing.

12

28. European Commission. Integrated Pollution Prevention and Control (IPPC) Reference

Document on Best Available Techniques in the Cement and Lime Manufacturing

Industries. Joint Research Centre, Institute for Prospective Technological Studies,

Technologies for Sustainable Development, European IPPC Bureau, World Trade Center,

Seville, Spain. March 2000.

29. Battye, R., and S. Edgerton, EC/R Incorporated, Chapel Hill, NC. Trip Report to

Mitsubishi Cement Corporation, Cushenbury Plant, Lucerne Valley, CA, December 2,

1999. Prepared for the U.S. EPA, RTP, NC, under contract No. 68-D-98-026, work

assignment No. 2-28. July 5, 2000.

30. Biggs, H.O., Plant Manager, Mitsubishi Cement Corporation. Biosolids Injection

Technology: An Innovation in Cement Kiln NOX Control. (no date). Received during

December 1999 trip report.

13

3.0 INDUSTRY DESCRIPTION

3.1 BACKGROUND

This chapter provides an overview of the cement industry, its annual production rates, and

the various manufacturing processes used. Process and operating parameters most influential for

NOX formation in the various processes are discussed.

The cement industry is a vital industry for a modern society because cement is an

essential ingredient in concrete. One need only mention reinforced-concrete walls and girders,

tunnels, dams, and roads to realize the dependence of our society upon cement products.

Hydraulic portland cement, the primary product of the cement industry, is made from clinker

blended with gypsum. Clinker is produced by heating a mixture of limestone, clay, and other

ingredients to incipient fusion at a high temperature. Limestone is the single largest ingredient

required in the cement-making process, and most cement plants are located near large limestone

deposits. Portland cement is used in almost all construction applications including homes, public

buildings, roads, industrial plants, dams, bridges, and many other structures.

In the cement-making process, the solid raw materials are heated to their fusion

temperature, typically 1400 to 1500 C (2550 to 2750 F), by burning various fuels such as coal.

Portland cement has been defined as “a hydraulic cement produced by pulverizing portland-

cement clinker and usually containing calcium sulfate.”1 Portland-cement clinker has been

defined as “a clinker, partially fused by pyroprocessing, consisting predominantly of crystalline

hydraulic calcium silicates.”1 Burning an appropriately proportioned mixture of raw materials at

a suitable temperature produces hard fused nodules called clinker which are further ground to a

desired fineness. Five types of portland cement are recognized in the United States which

contain varying amounts of the basic clinker compounds given in Table 3-1.2 Different types of

cements are produced by starting with appropriate kiln feed composition, blending the clinker

with the desired amount of calcium sulfate, and grinding the product mixture to appropriate

fineness. Manufacture of cements of all of the various types involves the same basic high

temperature fusion and clinkering process responsible for the NOX emissions from cement kilns.

3.2 TYPES OF CEMENT PRODUCED

The five basic types of portland cement recognized and produced in the United States are

described below.2,3 In addition, different varieties are prepared by using various blending

formulations.4

Type I portland cement is a normal, general-purpose cement suitable for all uses. It is

used in general construction projects such as buildings, bridges, floors, pavements, and other

precast concrete products. Type I is also known as regular cement and most commonly known as

gray cement because of its color. White cement typically contains less ferric oxide and is used

for special applications. There are other types of cements in general use such as oil-well cement,

14

quick-setting cement, and others for special applications. Type IA portland cement is similar to

Type I with the addition of air-entraining properties.

TABLE 3-1. BASIC CLINKER COMPOUNDS2

Formula Name

2CaOSiO2 Dicalcium silicate

3CaOSiO2 Tricalcium silicate

3CaOAL203 Tricalcium aluminate

4Ca0A1203Fe203 Tetracalcium aluminoferrite

Mg0 Magnesium oxide in free state or combined in di- or tricalcium silicate lattice.

Type II portland cement generates less heat at a slower rate and has a moderate resistance

to sulfate attack. Type II portland cements are for use where moderate heat of hydration is

required or for general concrete construction exposed to moderate sulfate action. Type IIA

portland cement is identical to Type II and produces air-entrained concrete.

Type III portland cement is a high-early-strength cement and causes concrete to set and

gain strength rapidly. Type III is chemically and physically similar to Type I, except that its

particles have been ground finer. It is made from raw materials with a lime to silica ratio higher

than that of Type I cement. They contain a higher proportion of tricalcium silicate (3Ca0Si02)

than regular portland cements. Type IIIA is an air-entraining, high-early-strength cement.

Type IV portland cement has a low heat of hydration and develops strength at a slower

rate than other cement types, making it ideal for use in dams and other massive concrete

structures where there is little chance for heat to escape. Type IV portland cement contains a

lower percentage of tricalcium silicate (3Ca0Si02) and tricalcium aluminate (3Ca0A1203) than

type I, thus lowering the heat evolution. Consequently, the percentage of dicalcium silicate is

increased substantially and the percentage of tetracalcium aluminoferrite (4Ca0A1203Fe203) may

be increased or may stay the same.

Type V portland cement is used only in concrete structure that will be exposed to severe

sulfate action, principally where concrete is exposed to soil and groundwater with a high sulfate

content. Type V portland cement are those which, by their composition or processing, resist

sulfates better than the other four types.

The use of air-entraining agents increases the resistance of the hardened concrete to

scaling from alternate freezing and thawing. By adding these materials to the first three types of

cements, IA, IIA, and IIIA varieties of cements are produced. Additional varieties of cements are

produced for special applications by blending different ingredients: masonry cement, expansive

cement, oil-well cement, etc. Masonry cements are commonly finely ground mixtures of

15

Figure 3-1. Annual clinker production. 5

portland cement, limestone, and air-entraining agents. Granulated blast furnace slags and natural

or artificial pozzolans are mixed and interground with portland cement to prepare still other

varieties such as blended types IP, IS, S, I(PM), and I(SM).4

3.3 INDUSTRY CHARACTERIZATION

3.3.1 Description of the Cement

Industry

About 77.6 million metric tons of

gray portland and 274,000 metric tons of

white cement were produced in a total of

198 cement kilns at 118 plants in the

United States in 1998.5 This was a 6.0

percent increase from the 1990 reported

total production of 73.5 million metric

tons. As shown in Figure 3-1, cement

industry annual clinker capacity steadily

declined from the 1975 peak through

1990 and has steadily increased since the

1990 low. While the number of kilns has

dropped off sharply, average kiln size has

increased. Since 1973 when average kiln

size was 173,000 metric tons, average kiln size has now reached 393,000 metric tons. Although

42 cement companies produced clinker in 1998, the top 5 companies provided about 44.2 percent

of the total finish grinding capacity. This is evidence of a high concentration of the U.S.

production among a limited number of top producers. Table 3-2 provides a list of all companies

along with their share of the total clinker production. Table 3-3 lists the clinker producing

capacity in the United States by States. The locations of the operating kilns are shown in

Figure 3-2. California and Texas are the two largest states in terms of clinker capacity with

Pennsylvania, Missouri, and Alabama rounding out the top five. Fourteen states and the District

of Columbia had no cement clinker- producing plants in 1998.5

TABLE 3-2. UNITED STATES CEMENT COMPANY CAPACITIES IN 1998

(INCLUDES GRAY AND WHITE PLANTS) 5

Rank Clinker

(103 tons/year)

Percent

Industry

Company Name

1

2

3

9371

8297

6459

12.0

10.6

8.3

Holnam Inc.

Southdown Inc.

Lafarge Corporation

TABLE 3-2. UNITED STATES CEMENT COMPANY CAPACITIES IN 1998 (continued)


Rank Clinker

(103 tons/year)

Percent

Industry

Company Name

16

4

5

6

4738

4367

3972

6.1

5.6

5.1

Ash Grove Cement Company

Blue Circle Inc.

Essroc Cement Corporation

7

8

9

3374

3119

3096

4.3

4.0

4.0

Lone Star Industries

Lehigh Portland Cement

Texas Industries

10

11

12

2965

2711

1616

3.8

3.5

2.1

California Portland Cement

RC Cement Company, Inc.

Centex

13

14

15

1580

1457

1387

2.0

1.9

1.8

Mitsubishi Cement Corporation

Kaiser Cement Corporation

Calaveras Cement Company

16

17

18

1358

1075

1047

1.7

1.4

1.3

Giant Cement Holding, Inc.

Kosmos Cement Company

St. Lawrence Cement Company

19

20

21

1003

1003

952

1.3

1.3

1.2

Texas-Lehigh Cement Company

Roanoke Cement Company

National Cement Company of Alabama

22

23

24

870

868

866

1.1

1.1

1.1

Sunbelt Cement Corporation

Capitol Cement Corporation

Pennsuco Cement Company

25

26

27

840

812

788

1.1

1.0

1.0

Allentown Cement Company Inc.

Dacotah Cement

Alamo Cement Company

28

29

30

768

763

755

1.0

1.0

1.0

North Texas Cement

Capitol Aggregates, Inc.

RMC Lonestar

31

32

33

639

567

562

0.8

0.7

0.7

Monarch Cement Company

Phoenix Cement Company

National Cement Company of California

TABLE 3-2. UNITED STATES CEMENT COMPANY CAPACITIES IN 1998 (continued)


Rank Clinker

(103 tons/year)

Percent

Industry

Company Name

17

34

35

36

545

545

498

0.7

0.7

0.6

Continental Cement Company, Inc.

Florida Crushed Stone

Dixon-Marquette

37

38

39

494

492

432

0.6

0.6

0.6

Rinker Portland Cement Corporation

Glens Falls Cement Company, Inc.

Rio Grande Cement Corporation

40

41

42

392

294

177

0.5

0.4

0.2

Dragon Products Company

Armstrong Cement & Supply Corporation

Royal Cement Company, Inc.

Total: 77914

TABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE


Clinker

(103

tons/year)

No. of

Facilities

Making

Clinker

No. of Kilns States

10461

8187

6809

4497

4233

10

10

10

5

5

18

19

21

7

6

California

Texas

Pennsylvania

Missouri

Alabama

TABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE (continued)


Clinker

(103

tons/year)

No. of

Facilities

Making

Clinker

No. of Kilns States

18

4228

3071

2745

2670

2632

3

4

3

4

4

8

7

4

8

8

Michigan

Florida

New York

Illinois

Indiana

2630

2462

1748

1728

1719

3

3

3

2

3

7

4

7

7

7

South Carolina

Iowa

Oklahoma

Arizona

Maryland

1710

1690

1259

1127

1104

4

3

2

2

2

11

5

2

3

3

Kansas

Colorado

Utah

Georgia

Ohio

1060

1044

1003

868

843

2

2

1

1

1

3

2

1

3

1

Tennessee

Washington

Virginia

West Virginia

Nebraska

812

794

759

726

623

1

1

1

1

2

3

3

1

1

3

South Dakota

Arkansas

Oregon

Kentucky

Nevada

TABLE 3-3. UNITED STATES 1998 CLINKER CAPACITIES BY STATE (continued)


Clinker

(103

tons/year)

No. of

Facilities

Making

Clinker

No. of Kilns States

19

593

585

433

432

392

2

1

1

1

1

2

2

1

1

1

Montana

Wyoming

Mississippi

New Mexico

Maine

237 1 2 Idaho

77914 105 192

There are no clinker producing plants in the following states:

Alaska Connecticut Delaware

Dist. of Columbia Hawaii Louisiana

Massachusetts Minnesota New Hampshire

New Jersey North Carolina North Dakota

Rhode Island Vermont Wisconsin

20

Figure 3-2. United States and Canadian Portland Cement Locations

(December 31, 1998)

21

The large majority of the cement plants (about 82.4 percent) in the United States are coal

fired with about 2.8 percent using natural gas, and 0.9 percent using oil as the primary fuel.5 The

remaining 13.9 percent of the plants used other combinations, e.g. coal/waste as primary fuel. In

1998, 11 plants used waste as a primary fuel with 49 plants reporting waste as an alternate fuel.

3.3.2 Overview of Cement Manufacturing Process

The process of portland cement manufacture consists of:6

• Quarrying and crushing the rock,

• Grinding the carefully proportioned materials to high fineness,

• Subjecting the raw mix to pyroprocessing in a rotary kiln, and

• Grinding the resulting clinker to a fine powder.

A layout of a typical plant is shown in Figure 3-3 which also illustrates differences

between the two primary types of cement processes: wet process and dry process.6 Newer

designs of dry process plants are equipped with innovations such as precalciners and/or

suspension preheaters to increase the overall energy efficiency of the cement plant.6 Figure 3-4 is

an illustration of a preheater/precalciner type of dry process system.7

The choice between the wet or dry process for cement manufacturing often depends upon

the moisture content in the raw feed materials mined from quarries. If the moisture content of

the feed materials is already very high (15 to 20 percent), a wet process may be attractive. The

recent trend, however, has been toward the dry process with preheater/precalciner systems. In

1998, about 20.6 million metric tons of clinker were produced by the wet process with 57.4

million metric tons produced by a dry process. Within the dry process category, 14.2 million

metric tons were produced by facilities equipped with a preheater system and 26.1 million metric

tons were produced by facilities equipped with a precalciner system.5

The different steps involved in the cement manufacturing process are described in the

following subsections.

3.3.3 Raw Materials and Kiln Feed Preparation

Calcium carbonate and the oxides of silicon, aluminum, and iron comprise the basic

ingredients of cement raw mix. Because of the large requirement for calcium, the plants are

generally located near the source of the calcareous material. The requisite silica and alumina

may be derived from a clay, shale, or overburden from a limestone quarry. Such materials

usually contain some of the required iron oxide, but many plants need to supplement the iron

with mill scale, pyrite cinders, or iron ore. Silica may be supplemented by adding sand to the

22

Figure 3-3. Steps in the manufacture of portland cement. 7

23

Figure 3-4. Preheater/precalciner cement kiln. 7

24

raw mix, whereas alumina can be furnished by bauxites and alumina-rich flint clays.6 Industrial

byproducts are becoming more widely used as raw materials for cement, e.g., slags contain

carbonate-free lime, as well as substantial levels of silica and alumina. Fly ash from utility

boilers can often be a suitable feed component, since it is already finely divided and provides

silica and alumina.

The bulk of raw materials originates in the plant quarry. A primary jaw or roll crusher is

frequently located within the quarry and reduces the quarried limestone or shale to about 100 mm

top size. A secondary crusher, usually roll or hammer mills, gives a product of about 10 to 25

mm top size. Combination crusher-dryers can utilize exit gases from the kiln or clinker cooler to

dry wet material during crushing. Each of the raw materials is stored separately and proportioned

into the grinding mills separately using weigh feeders or volumetric measurements. Ball mills

are used for both wet and dry processes to grind the material to a fineness such that only 15 to 30

wt% is retained on a 74-m (200 mesh) sieve.

In the wet process the raw materials are ground with about 30 to 40 percent water,

producing a well-homogenized mixture called slurry. Raw material for dry process plants is

ground in closed-circuit ball mills with air separators, which may be adjusted for the desired

fineness. Drying may be carried out in separate units, but most often is accomplished in the raw

mill simultaneously with grinding. Waste heat can be utilized directly in the mill by coupling the

raw mill to the kiln or clinker cooler exhaust. For suspension preheater-type kilns, a roller mill

utilizes the exit gas from the preheater to dry the material in suspension in the mill. A blending

system provides the kiln with a homogeneous raw feed. In the wet process the mill slurry is

blended in a series of continuously agitated tanks in which the composition, usually the calcium-

oxide content, is adjusted as required. These tanks may also serve as kiln feed tanks or the slurry

may be pumped to large kiln feed basins. Dry process blending is usually accomplished in a silo

with compressed air.6

3.3.4 Pyroprocessing

All cement clinker is produced in large rotary kiln systems. The rotary kiln is a refractory

brick-lined cylindrical steel shell [3 to 8 m (10 to 25 ft) dia, 50 to 230 m (150 to 750 ft) long]

equipped with an electrical drive to rotate the kiln on its longitudinal axis at 1 to 3 rpm. It is a

countercurrent heating device slightly inclined to the horizontal so that material fed into the

upper end travels slowly by gravity to be discharged into the clinker cooler at the lower,

discharge end. The burners at the firing end, i.e., the lower or discharge end, produce a current of

hot gases that heats the clinker, and the calcined and raw materials in succession as it passes

upward toward the feed end. Refractory bricks of magnesia, alumina, or chrome-magnesite

combinations line the firing end. In the less heat-intensive midsection of the kiln, bricks of lower

thermal conductivity are often used. Abrasion-resistant bricks or monolithic castable linings are

used at the feed end.6

25

Pyroprocessing may be conveniently divided into four stages, as a function of location

and temperature of the materials in the rotary kiln.8

1. Evaporation of uncombined water from raw materials, as material temperature

increases to 100C (212F);

2. Dehydration, as the material temperature increases from 100C to approximately

430C (800F) to form oxides of silicon, aluminum, and iron;

3. Calcination, during which carbon dioxide (CO2) and CaO are formed from

calcium carbonates, primarily between 900C (1650F) and 982C (1800F); and

4. Reaction, of the oxides in the burning zone of the rotary kiln, to form cement

clinker at temperatures of approximately 1510C (2750F).

The duration and location of these stages in an actual kiln depend upon the type of

process used, e.g., wet or dry, and the use of preheaters and precalciners as discussed in the

following section.

It is desirable to cool the clinker rapidly as it leaves the burning zone. Heat recovery,

preheating of combustion air, and fast clinker cooling are achieved by clinker coolers of the

reciprocating-grate, planetary, rotary, or shaft type. Most commonly used are grate coolers where

the clinker is conveyed along the grate and subjected to cooling by ambient air, which passes

through the clinker bed in cross-current heat exchange. The air is moved by a series of

undergrate fans and becomes preheated to 370 to 800 C (700 to 1500 F) at the hot end of

cooler. A portion of the heated air serves as secondary combustion air in the kiln. Primary air is

that portion of the combustion air needed to carry the fuel into the kiln and disperse the fuel.6

3.3.4.1 Wet Process Kilns. In a long wet-process kiln, the slurry introduced into the feed

end first undergoes simultaneous heating and drying. The refractory lining is alternately heated

by the gases when exposed and cooled by the slurry when immersed; thus, the lining serves to

transfer heat as do the gases themselves. Large quantities of water must evaporated, thus most

wet kilns are equipped with chains suspended across the cross section of the kiln to maximize

heat transfer from the gases to the slurry. After most of the moisture has been evaporated, the

nodules, which still contain combined water, move down the kiln and are gradually heated to

about 550 C (1022F) where the calcination reactions commence. The calcined material further

undergoes clinkering reactions. As the charge leaves the burning zone and begins to cool, clinker

minerals crystallize from the melt, and the liquid phase solidifies. The granular clinker material

drops into the clinker cooler for further cooling by air.6

Wet kilns typically represent an older cement technology with smaller capacity kilns. In

the United States wet cement kiln capacities range from 77,000 to 1,179,000 metric tons/year

with an average of 307,000 metric tons/year.5

26

3.3.4.2 Dry Process Kilns. The dry process utilizes a dry kiln feed rather than a slurry.

Early dry process kilns were short, and the substantial quantities of waste heat in the exit gases

from such kilns were frequently used in boilers to generate electric power which often satisfied

all electrical needs of the plant. In one modification, the kiln has been lengthened to nearly the

length of wet-process kilns and chains were added. The chains serve almost exclusively a heat-

exchange function. Refractory heat -recuperative devices, such as crosses, lifters, and trefoils,

have also been installed. So equipped, the long dry kiln is capable of better energy efficiency

than wet kilns. Other than the need for evaporation of water, its operation is similar to that of a

wet kiln. To improve the energy efficiency of the dry process, variations such as suspension

preheaters and precalciners have been introduced as discussed in the next sections.6

Long dry process kilns are generally of a smaller capacity compared to long wet kilns. In

the United States dry cement kiln capacities range from 50,000 to 590,000 metric tons/year with

an average capacity of 265,000 metric tons/year.5

3.3.4.3 Suspension Preheaters. In systems with suspension preheaters, the dry,

pulverized feed passes by gravity through a series of cyclones in a vertical arrangement where it

is separated and preheated several times, typically in a four-stage cyclone system. The partially

(40 to 50 percent) calcined feed exits the preheater tower into the kiln at about 800 to 900 C

(1500 to 1650 F). The kiln length required for completion of the cement formation is

considerably shorter than that of conventional kilns, and heat exchange is very good. Suspension

preheater kilns are very energy efficient compared to wet or long dry kilns. The intimate mixing

of the hot gases and feed in the preheaters promotes condensation of alkalies and sulfur on the

feed which sometimes results in objectionable high alkali and sulfur contents in the clinker. To

alleviate this problem, some of the kiln exit gases can bypass the preheater through a slip stream

or fewer cyclone stages can be used in the preheater with some sacrifice of efficiency.6

Suspension preheater kilns represent a newer cement technology compared to the long

dry kilns. They are also somewhat larger in production capacity than the long conventional

rotary kilns. In the United States the preheater type kiln capacities range from 223,000 to

1,237,000 metric tons/year with an average capacity of 406,000 metric tons/year.5

3.3.4.4 Precalciner Systems. The success of preheater kiln systems, led to precalciner

kiln systems. These units utilize a second burner to carry out calcination in a separate vessel

attached to the preheater. The calciner utilizes preheated combustion air drawn from the clinker

cooler or kiln exit gases and is equipped with a burner that burns about 60 percent of the total

kiln fuel. Most often coal is used as a fuel in a calciner furnace; however, almost any fuel may

be used including chipped tires. The raw material is calcined almost 95 percent, and the gases

continue their upward movement through successive cyclone preheater stages in the same

manner as in an ordinary preheater. The precalciner system permits the use of smaller dimension

kilns since only actual clinkering is carried out in the rotary kiln. Energy efficiency is even better

than that of a preheater kiln, and the energy penalty for bypass of kiln exit gases is reduced since

27

only about 40 percent of the fuel is being burned in the kiln. The burning process and the clinker

cooling operations for the modern dry-process kilns are the same as for long wet kilns.6

The precalciner technology is the most modern cement manufacturing technology and

almost all of the newer cement plants are based on these designs. Precalciner kilns are also much

larger in capacity than the conventional rotary kilns. The precalciner type kilns in the United

States range from 449,000 to 1,580,000 metric tons/year with an average of 869,000 metric

tons/year.5 Because of the new large precalciner plants replacing older and smaller plants, the

overall average kiln capacity has been steadily increasing in the United States. It has increased

from an average of 239,000 metric tons/year in 1980 to an average capacity of 393,000 metric

tons/year in 1989.5

3.3.5 Finish Grinding

The cooled clinker is conveyed to clinker storage. It is subsequently mixed with 4 to 6

percent gypsum and introduced directly into the finish mills. These are large, steel cylinders [2

to 5 m (7 to 16 ft) in diameter] containing a charge of steel balls, that rotate at about 15 to 20

rpm. The clinker and gypsum are ground to a fine, homogeneous powder. About 85 to 96

percent of the product is in particles less than 44 m in diameter. This grinding may be

accomplished by two different mill systems. In open-circuit milling, the material passes directly

through the mill without any separation. A wide particle size distribution range is usually

obtained with substantial amounts of very fine and rather coarse particles. Open circuit grinding

is, however, rarely practiced in U.S. cement plants. In closed-circuit grinding, the mill product is

carried to a cyclonic air separator in which the coarse particles are rejected from the product and

returned to the mill for further grinding.6

3.3.6 Quality Control

Beginning at the quarry operation, quality of the end product is maintained by

adjustments of composition, burning conditions, and finish grinding. Control checks are made

for fineness of materials, chemical composition, and uniformity. Clinker burning is monitored

by the liter weight test weighing a portion of sized clinker, a free lime test, or checked by

microscopic evaluation of the crystalline structure of the clinker compounds. Samples may be

analyzed by wet chemistry, X-ray fluorescence, atomic absorption, or flame photometry.

Standard cement samples are available from the National Institute of Standards and Technology.

Fineness of the cement is most commonly measured by the air permeability method. Finally,

standardized performance tests are conducted on the finished cement.6

3.3.7 Emission Control Systems

All cement plants are equipped with particulate collection devices to remove cement kiln

dust (CKD) from the kiln exhaust gases and clinker dust from clinker cooler exhaust gases.

Several small dust collectors are also installed at various dust emission points throughout the

28

1. American Society for Testing and Materials. 1998 Annual Book of ASTM Standards.

ASTM Volume 04.01 Cement; Lime; Gypsum. West Conshohocken, PA. 1998.

2. Shreve, R.N., and J.A. Brink. Chemical Process Industries. Fourth Edition. New York,

NY. McGraw Hill, Inc. 1977. pp. 156-162.

3. Dorris, V.K., A. Gerson, and M.McIntyre. Portland Cement Association. Cement and

Concrete Reference Guide. Skokie IL. 1997.



NC. March 1994.


Information Summary, December 31, 1998. Skokie, IL. 214 pp.


Encyclopedia of Chemical Technology. Vol. 5. Fourth Edition. New York, NY. John

Wiley & Sons, Inc. 1992. pp. 564-598.

7. Kosmatka, S.H. and W.C. Panarese. Design and Control of Concrete Mixtures,

Thirteenth Edition. Portland Cement Association. Skokie, IL. 1994.


AP-42. Fifth Edition. Volume I - Stationary Point and Area Sources. Research Triangle

Park, NC. January 1995. pp. 11.6-1 - 11.6-26.

plant such as material transfer points and grinding operations. The collected CKD is usually

recycled with the feed or injected at different points in the kiln depending upon the quality and

source of the CKD. None of the cement plants in the United States uses any flue gas treatment

for reducing NOX, emissions.

3.4 REFERENCES

29

4.0 UNCONTROLLED NOX EMISSIONS

4.1 MECHANISMS OF NOX FORMATION IN CEMENT MANUFACTURING

In cement manufacturing, conditions favorable for formation of nitrogen oxides (NOX)

are reached routinely because of the high process temperatures involved. Essentially, all of the

NOX emissions associated with cement manufacturing are generated in the cement kilns.

Although, there are other heating operations in a cement plant, such as drying of raw feed or coal,

often the heat from the kiln exhaust gases is used for these operations making their contribution

to NOX emissions negligible.

In cement kilns, NOX emissions are formed during fuel combustion by two primary

mechanisms:

• Oxidation of the molecular nitrogen present in the combustion air which is termed

thermal NOX formation, and

• Oxidation of the nitrogen compounds present in the fuel which is termed fuel NOX

formation.

Sometimes the raw material feed to the kiln may also contain nitrogen compounds which may

lead to feed NOX formation similar to fuel NOX formation. Because of the high temperatures

involved in the burning or clinker formation step, the thermal NOX formation provides the

dominant mechanism for NOX formation in cement manufacturing. The term NOX includes both

NO and NO2 species, although NO2 normally accounts for less than 10 percent of the NOX

emissions from a cement kiln exhaust stack.1 The concentration and emission of NOX are,

however, typically expressed in equivalent NO2 form.

4.1.1 Thermal NOX Formation

Thermal NOX is formed by the homogeneous reaction of oxygen and nitrogen in the gas

phase at high temperatures. In the overall reaction mechanism proposed by Zeldovich,2 the two

important steps in NO formation are given as:

N2 + O NO + N kf = 2 x 1014 exp(-76500/RT) (4-1)

N + O2 NO + O kf = 6.3 x 109 exp(-6300/RT) (4-2)

where kf are the rate constants for the reactions shown. The high activation energy of reaction

(4-1), 76.5 kcal/mol, means that this reaction is the most temperature sensitive. An equilibrium

reaction of NO with O2 further results in NO2 formation.

30

The equilibrium concentrations of NO and NO2 formed thus depend strongly upon the

gas-phase temperature as well as the concentration of O2 and N2 in the gas phase. Table 4-1

shows the equilibrium concentrations of NO and NO2 for two conditions.3 First, the equilibrium

concentrations of NO and NO2 for N2 and O2 concentrations found in ambient air are shown.

Secondly, Table 4-1 also shows the NO and NO2 concentrations at flue gas conditions where the

O2 and N2 concentrations are defined for this table as 3.3 percent O2 and 76 percent N2. The

equilibrium NO concentrations for the flue gas conditions are lower than those for ambient

conditions due to the lower O2 concentration. The excess air used during fuel combustion can

substantially affect NO formation by determining the amount of oxygen available for NO

reaction. The cement kiln burning zones usually have about 5 to 10 percent excess air while

higher excess air levels are not uncommon. Figure 4-1 shows the theoretical equilibrium

concentrations of NO in the flue gas for different excess air levels.1 As can be seen from this

figure, over 1000 ppm of NO may possibly be formed at the typical kiln solids temperatures of

1430 to 1480 C (2600 to 2700 F) as the corresponding gas-phase temperatures are on the order

of 1650 C (3000 F).

TABLE 4-1. CALCULATED EQUILIBRIUM CONCENTRATIONS (in ppm)

OF NO AND NO2 IN AIR AND FLUE GAS 3

Temperature Air Flue Gas

K F NO NO2 NO NO2

300 80 3.4 (10)-10 2.1 (10)-4 1.1 (10)-10 3.3 (10)-3

800 980 2.3 0.7 0.8 0.1

1440 2060 800 5.6 250 0.9

Fuel combustion in the kiln burning zone is the primary source of thermal NOX,

formation in cement kilns due to temperatures well above 1400 C (2550 F). In contrast, the

fuel combustion temperature in a precalciner or in a kiln riser duct is well below 1200 C

(2200 F), suppressing thermal NOX formation.4 Mainly fuel and feed NOX may be formed in

the secondary firing zone of preheater and precalciner kiln systems. Along with the combustion

temperature, the gas-phase residence time and the available oxygen concentration in the high

temperature kiln burning zone are important parameters. Longer residence times at the high

temperatures will allow the NO to be formed in the equilibrium quantities. Greater amounts of

oxygen in the combustion zone will of course lead to greater amounts of NO formation. Once

formed, the decomposition of NO at lower temperatures, although thermodynamically favorable,

is kinetically limited. Thus, strategies to reduce NOX emissions need to be based upon reducing

formation of NOX which may be achieved by reducing combustion temperature, oxygen

concentration in the high temperature combustion zone, and the gas residence time at high

temperatures.

31

Figure 4-1. Theoretical equilibrium concentrations

of NO in gas from combustion sustained in air.1

4.1.2 Fuel NOX Formation

Fuel NOX is formed by the

conversion of nitrogen present in the fuel

used. A recent survey of the cement

industry by Portland Cement Association

(PCA) indicates that almost 82 percent of

the energy requirement of the cement

industry is provided by coal.5 Natural gas

contributed about 3 percent of the energy

demand, oil about 1 percent, and other

fuels such as waste solvents provided

about 14 percent of the energy. Both oil

and natural gas have relatively low fuel-

bound nitrogen content, whereas coal may

contain 1 to 3 percent of nitrogen by

weight depending upon the source of coal.

Waste-derived fuels (WDF) such as scrap

tires, used motor oils, surplus printing

inks, dry-cleaning solvents, paint thinners,

sludge from the petroleum industry,

agricultural wastes such as almond shells,

and even municipal biosolids (dewatered

sewage sludge) are finding an increasing

application in the cement kilns.6 The nitrogen content in these fuels may be significant

depending on the chemicals included in the waste mix being burned.

The maximum possible fuel NOX formation may be estimated from the fuel nitrogen

content by assuming 100 percent nitrogen conversion. As discussed in section 4.3, the typical

heat requirement for a wet process is estimated to be about 6 million Btu for a ton of clinker and

the corresponding requirement for a dry process is estimated to be about 4.5 million Btu for a ton

of clinker. Assuming an average heat requirement of 5.3 million Btu for a ton of clinker, and a

coal heating value of 12,000 Btu/lb, about 442 lb of coal will be required per ton of clinker

produced. With a nitrogen content of 1 percent by weight, approximately 9.5 lb of NO (14.5 lb

expressed as NO2) would be produced per ton of clinker with 100 percent nitrogen conversion.

Thus, even with only 10 percent conversion of coal nitrogen to NOX, 1.5 lb of fuel NOX

(expressed as NO2) may be formed per ton of clinker when coal is used as a primary fuel.

The amount of fuel NOX formed is difficult to identify separately from thermal NOX as

measurements indicate the overall NOX formed. In general, however, thermal NOX is assumed to

be the dominant mechanism in cement kilns.7 Typically, gas burners produce more intense and

hot flames compared to the less intense "lazy" flames produced by coal burners. Thus, gas-fired

kilns may be expected to produce greater thermal NOX as compared to coal-fired kilns. Coal, on

32

the other hand, contains much greater amounts of fuel-bound nitrogen than natural gas which has

almost no fuel-bound nitrogen. The coal-fired kilns may thus be expected to produce more fuel

NOX than gas-fired kilns. A study of gas- and coal-fired kilns, however, clearly indicated that

gas-fired, dry-process kilns typically produce almost three times more NOX than the coal-fired,

dry-process kilns.7 This fact indicates the dominance of thermal NOX in overall NOX formation.

4.1.3 Feed NOX Formation

Similar to coal, the raw materials used in cement production may contain a significant

amount of nitrogen. In most cases, limestone is the major raw material, with the remainder of the

raw mix being composed of clays, shales, sandstones, sands, and iron ores. Since most of these

raw material components are sedimentary minerals, they may contain small amounts of

chemically bound nitrogen, presumably of organic origin. Various kiln feeds contain appreciable

amounts of nitrogen, ranging from about 20 ppm up to as much as 1000 ppm (as N).8 The higher

values (>100 ppm) are generally associated with minerals displaying noticeable kerogen

contents. Since 100 ppm N in a kiln feed is equivalent to about 1 lb NOX per ton of clinker (if it

all converted), NOX emissions from the kiln feed may represent a major source of NOX from

cement kilns. Nevertheless, it is probably less important than thermal NOX and fuel NOX in most

cases.

The same study indicated that conversion of feed nitrogen to NOX occurs mainly in the

300 to 800 C (570 to 1470 F) temperature range and depends upon the feed heating rate.8

Rapid heating rates (~1000 C flash heating) of the kiln feed mixtures were found to give much

lower conversion efficiencies, whereas slow heating rates of kiln feed mixtures (~60 C/min)

gave fairly high conversion of about 50 percent of bound nitrogen to NO. These results were

explained by assuming that the organic nitrogen must vaporize from the sample prior to

oxidation if high conversion efficiencies to NOX are to be achieved. If heating rates are rapid,

"cracking" of these volatile compounds may occur in situ, and this may result in conversion of

the bound nitrogen directly to N2 before it comes into contact with gaseous oxygen, thus reducing

the fraction converted to NOX. Such a hypothesis is also consistent with the observation that,

during coal combustion, the involatile or "char" nitrogen is converted to NOX much less

efficiently than the volatile nitrogen.9

4.2 FACTORS AFFECTING NOX EMISSIONS IN CEMENT MANUFACTURING

Chapter 3 identified four different types of cement kilns used in the industry: wet kilns,

long dry kilns, kilns with a preheater, and kilns with a preheater/precalciner. The wet and long

dry kilns typically have only one fuel combustion zone, whereas the newer preheater and

precalciner kiln designs have two or three fuel combustion zones: kiln burning zone, riser duct

and precalciner. Because the typical temperatures present in the combustion zones are different,

the factors affecting NOX formation are also somewhat different in different kiln types and are

discussed in the following sections. In addition to the specific NOX formation mechanisms, the

energy efficiency of the cement-making process is also important as it determines the amount of

33

heat input needed to produce a unit quantity of cement. A high thermal efficiency would lead to

less consumption of heat and fuel, and would generally produce lower NOX emissions.

4.2.1 NOX Formation in the Kiln Burning Zone

In the kiln burning zone, thermal NOX provides the primary mechanism for NOX

formation. Thermal NOX formation depends upon the combustion zone temperature, the gas-

phase residence time and the oxygen concentration in the high temperature combustion zone.

The flame temperature strongly depends upon the type of fuel burned. The temperature and

intensity are generally greater for gas burners than coal burners. The oxygen concentration in the

combustion zone depends upon the overall excess air used and on the source and proportion of

primary and secondary combustion air. Less primary air may produce an initial

high-temperature, fuel-rich combustion zone followed by a low-temperature fuel-lean

combustion zone. Such a combination is likely to reduce NOX formation.

The firing system used in the kiln affects the proportion of primary and secondary

combustion air. Direct firing systems introduce a large proportion of combustion air with the

fuel being burned. This produces two conflicting effects for NOX emissions: higher oxygen

concentration or fuel lean combustion and lower gas temperature. Indirect firing systems on the

other hand use only a small portion of combustion air to convey fuel and thus use less primary

air. In general, direct fired systems may be expected to produce greater NOX emissions compared

to indirect fired systems. The majority of kilns in the United States are direct fired.

The flame shape and the theoretical flame temperature are important factors in thermal

NOX formation as these factors determine the hottest points in the flame. A long "lazy" flame

will produce less NO than a short intense flame. The flame shape depends on the fuel being

burned as well as the proportion of air. For the same amount of primary air, gas burning may be

expected to produce a shorter and more intense flame than coal burning. The lower the

secondary air temperature and the greater the dust content in the secondary air, the lower the NOX

formation in the kiln burning zone. A large amount of water in the primary air (from a direct

firing coal mill) and injection of cement kiln dust (CKD) in the burning zone (insufflation) may

also reduce NOX formation. With increasing excess air percentage, the NOX formation in the kiln

will increase, but only up to a certain point as an increasing excess air rate will reduce the

secondary air temperature and, consequently, the flame temperature.

Process conditions that can affect NOX emissions substantially are: temperature stability,

stability of raw mix feed rate, burnability of raw mix, and alkali and sulfur control. Temperature

stability is important to maintain the quality of clinker and is achieved by stable-flame conditions

and energy efficiency. Clinker formation reactions require temperatures of 2650 to 2800F

(1450 to 1540C )10 and an oxidizing environment. Sometimes natural gas or liquid waste-

derived fuel is used to control flame conditions and improve clinker quality. The excess air used

during combustion has a substantial influence on NOX emissions. Oxygen levels of 4 to 5

percent in kiln exhaust gases would correspond to high NOX emissions, whereas oxygen levels of

34

only 0.5 to 1.5 percent would mean lower NOX emissions. Thus, NOX emissions in a kiln may

depend upon the care exercised by the operator in minimizing excess oxygen needed to maintain

the quality of the clinker produced. All but one of the clinker formation reactions are exothermic

and represent a dynamic process that requires constant operator adjustments which can vary NOX

formation.

The heating value of the fuel burned may also affect NOX emissions. High heating value

fuels, such as petroleum coke, require less combustion air and produce less NOX per ton of

clinker.

Different raw material compositions require different burning conditions to maintain the

quality of clinker produced. Thus, similar types of kilns with different feed materials may

produce different levels of NOX emissions. The alkali content of finished cement needs to be

below a certain acceptable level. Low alkali requirements may require higher kiln temperatures

and longer residence times at high temperatures to volatilize the alkali present in the molten

clinker. Raw materials with greater alkali content may need to be burned longer at higher

temperatures to meet alkali requirements and thus may produce greater NOX emissions.

Increased volatilization of alkali results in increased alkali emissions in kiln exhaust gases. To

control alkali emissions, a part of the kiln exhaust gases may be bypassed around a downstream

unit, e.g., a precalciner. The bypassed gases are quenched to remove alkali and sent through a

particulate matter collector. This alkali-rich particulate matter is removed from the process and

disposed. The bypass of kiln exhaust gases typically involves a fuel penalty, e.g., about 20,000

Btu/ton of clinker for every 1 percent gas bypass. The additional heat requirement will

contribute to increased NOX emissions.

Wet kilns require about 33 percent more thermal energy than a dry kiln. This means a

greater volume of exhaust gas from a wet kiln for the same production. On the other hand, the

greater amount of combustion air will also mean a somewhat lower secondary air temperature.

Based on these contradicting factors, one might expect the NOX emissions from a wet process

kiln to be similar to the dry and preheater kilns without riser duct firing.

4.2.2 NOX Formation in Secondary Firing

In the secondary firing region of precalcining kilns, where temperatures range from 820 to

1100 C (1500 to 2000 F) , the following reactions may take place:

"N" + O NO (4-3)

"N" + NO N2 + O (4-4)

where "N" means nitrogen originating from nitrogen compounds in the fuel.1 Reaction (4-3)

shows that NO formation in the secondary firing zone will depend upon the nitrogen content in

the fuel and the oxygen level in the firing zone. Reaction (4-4) indicates that, if there is already

35

NO present in the gas introduced into the secondary firing zone, a reduction of this NO may

occur with the fuel nitrogen compounds acting as reducing agents. Accordingly, the net

formation of NO in the secondary firing zone will also depend upon the initial NO concentration

in the combustion gas. Finally, measurements have shown that the volatile content in the solid

fuel and the temperature in the secondary firing zone also influence the NO formation in the

secondary firing zone.11 With increased volatile content in the fuel, the ratio of fuel nitrogen

conversion into NO seems to decrease and, as the reaction rate of reaction (4-4) increases more

rapidly with the temperature than that of reaction (4-3), an increase in the temperature of the

secondary firing region may reduce-the net NOX formation.1

4.2.2.1 Suspension Preheater (SP) Kilns with Riser Duct Firing. In many SP kiln

systems 10 to 20 percent of the fuel is fired into the riser duct. The preheater systems are more

energy efficient compared to long dry kilns. The increased energy efficiency and the reduction in

the amount of fuel burned at the higher clinker burning temperature may be expected to reduce

the NOX emissions from preheater kilns when compared with the long dry and wet kilns.

Measurements at several riser-duct fired kiln systems indicate that firing coarse fuel (e.g., tires)

into the kiln riser duct will reduce NOX emissions from the kiln systems.12 This may be

explained by the fact that a large part of the fuel falls directly down into the kiln charge, creating

a reducing atmosphere in the kiln back-end where NOX from the burning zone is reduced.

Conversely, when firing finely ground fuel into the kiln riser duct, the NOX content in the

exhaust gas may increase on passing through the riser duct. As the NOX emissions from the kiln

may also increase slightly due to an increased excess air rate, the total NOX emissions from the

kiln system may increase when starting up riser duct firing with finely ground fuel.1

4.2.2.2 Precalcining Kiln Systems. In precalcining kiln systems with a tertiary air duct,

firing into the rotary kiln typically accounts for only 40 to 50 percent of the total heat

consumption and the specific amount of combustion gases from the kiln burning zone is reduced

proportionally. Precalciner kilns also typically require the least amount of energy per unit

amount of clinker produced. The lower energy requirement and the substantial reduction in the

proportion of the fuel burned at clinker burning temperatures may be expected to reduce the NOX

emissions from the precalciner kilns as compared to the preheater kilns. On the other hand, the

NOX concentration (in ppm) in the kiln gas may be considerably higher than in preheater kilns.

This is probably due to the shorter material and longer gas retention times in the precalciner kiln

burning zone combined with a very high secondary air temperature.1

When examining the contribution from the calciner firing to the emission of NOX, two

basically different types of precalcining kiln systems need to be considered:

• The in-line (ILC) type in which the kiln gas passes through the firing region of the

precalciner, and

36

• The separate line (SLC) type in which the kiln exhaust gas bypasses the firing

region of the precalciner.

ILC systems: In these systems, the fuel combustion in the calciner takes place in a

mixture of the kiln exhaust gas and hot air from the cooler (tertiary air). Some of the nitrogen in

the fuel reacts with NO from the kiln exhaust gas while another part reacts with oxygen to form

NO. The result may be a net increase or a net reduction of NO in the calciner.

SLC systems: In these systems, the fuel combustion in the calciner takes place in pure hot

air. In the case of oil firing, NO production in the calciner is negligible; but when using fuels

containing fuel-bound nitrogen, up to 50 percent of the nitrogen compounds in the fuel may be

converted into NOX. The specific NOX, production in an SLC calciner may be as high as 4 lb

NOX per ton of clinker as measured in a calciner fired with petroleum coke which has a high

nitrogen content and low volatile content.1 The NOX in the calciner exhaust gas is added to the

NOX in the gas from the rotary kiln which leaves this type of kiln system without being reduced.

When fired with solid fuels, SLC systems may therefore be expected to generate somewhat

higher NOX emissions than the ILC systems.1

4.2.3 Energy Efficiency of the Cement-Making Process

Since NOX formation is directly related to fuel combustion, any reduction in the amount

of fuel burned per unit amount of clinker produced should reduce NOX emissions per unit

clinker. Attempts to improve energy efficiency of the process by avoiding excessive clinker

burning and utilizing waste heat effectively for preheating combustion air, coal, and raw mix is

likely to reduce NOX emissions. Improving heat transfer between hot gases and solid materials,

e.g., by chain systems, will improve energy efficiency. The newer preheater and precalciner kiln

designs provide very efficient preheating and precalcining of the raw mix with intimate gas-

solids contact in cyclone towers. New cement kiln installations or renovations of older kilns thus

predominantly involve precalciner designs for their energy efficiency. The inherent energy

efficiency of these kiln designs is likely to produce less NOX emissions per unit amount of

clinker as compared to the wet or long dry kilns.

4.3 AVAILABLE DATA FOR UNCONTROLLED NOX EMISSIONS FROM CEMENT

MANUFACTURING FACILITIES

The four types of cement kilns discussed in the last section exhibit different combustion

characteristics as well as energy efficiencies and heat requirements. The available NOX

emissions data are therefore generally grouped by these cement kiln types.

In January 1995, EPA published a revised AP-42 section for Portland Cement

Manufacturing.13 The revised NOX emission factors adopted for the AP-42 document for the

same four kiln types mentioned above are: 7.4 lb/ton of clinker for wet process kilns, 6.0 lb/ton

of clinker for dry process kilns, 4.8 lb/ton of clinker for kilns with preheaters, and 4.2 lb/ton of

1 A = Tests are performed by a sound methodology and are reported in enough detail for adequate

validation.

B = Tests are performed by a generally sound methodology, but lacking enough detail for

adequate validation.

C = Tests are based on an unproven or new methodology, or are lacking a significant amount of

background information.

D = Tests are based on a generally unacceptable method, but the method may provide an order-

of-magnitude value for the source.

2 Waste Derived fuels can include scrap tires.

37

clinker for kilns with precalciners. These emission factors were developed from 23 references.

All 23 references are over ten years old and primarily represent short-term compliance tests.

Each AP-42 emission factor is given a rating from A through E, with A being the best.

Two steps are involved in factor rating determination. The first step is an appraisal of data

quality, the reliability of the basic emission data that will be used to develop the factor. The

second step is an appraisal of the ability of the factor to stand as a national annual average

emission factor for that source activity. All of the AP-42 NOX emission factors have a “D” rating

which is below average. A “D” rating means the factors were developed from A-, B-, and/or C -

rated test data from a small number of facilities, and there may be reason to suspect that these

facilities do no represent a random sample of the industry.1 There also may be evidence of

variability with the source population.

During preparation of the 1994 ACT document, NOX emissions data were collected from

major cement companies in the United States. Out of 51 cement kilns providing NOX emissions

data, 22 were from wet kilns, 10 were from long dry kilns, 10 were from preheater kilns, and 9

were from precalciner type cement kilns. Table 4-2 presents the NOX emissions data along with

the kiln types and fuels burned.

As seen from Table 4-2, in general, wet kilns were found to produce the highest NOX

emissions ranging from 3.6 to 19.5 lb NOX/ton of clinker with an average of 9.7 lb NOX/ton of

clinker. Wet kilns also consume the most energy among different cement kiln types. The energy

consumption of wet kilns was found to be in the range of 4.9 to 8.8 MM Btu/ton of clinker with

an average of 6.0 MM Btu/ton. Wet kilns burning gas were found to produce greater NOX

emissions as compared to those burning coal. Also in some cases, high secondary combustion air

temperatures were present with high NOX emission rates. Twelve of the wet kilns reported

burning WDFs2 in significant quantities. Five of these kilns used "mid-kiln" firing of the solid

and liquid waste fuel and the other seven kilns injected liquid waste in the hot kiln burning zone.

CEM = Continuous emissions monitor; WDF - waste derived fuel; LWDF - liquid waste derived fuel; SWDF - solid waste derivedfuel; either WDF or SWDF can include waste tires 38

TABLE 4-2. NOX EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT

Location Kiln # Kiln type Capacity

(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference

1. Ash Grove Cement Co.

Foreman, AR 1

2

3

Wet

Wet

Wet

36

36

54

42% - Coal42% - LWDF16% - SWDF

As above

As above

6.86

7.1

7.05

13.51

18.34

15.65

CEMJul-92

CEMJul-92

CEMJul-92

14

14

14

Chanute, KS 1 & 2 Wet 30% - Coal7.1% - Coke61.6% - WDF1.3% - Gas

6.56 9 CEM7/10/927/18/92

14

Durkee, OR 1 Four-stagePreheater

68.2 100% - Coalduring tests95% - GasCurrently

3.88during test3.72currently

5.06 CEMMethod 79/15/85

14

Nephi, UT 1 Precalciner 80 100% - Coal 3.6 3.434.511.31

Nov-82Jul-88Apr-92

14

TABLE 4-2. NOX EMISSIONS DATA USED TO DEVELOP 1994 ACT DOCUMENT (continued)


(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


2. Blue Circle Inc.

Calera, AL 1 Dry 38 100% - Coal 3.8 9.58 CEM15

Atlanta, GA 1 Dry 38.5 50% - Coal50% - Coke

3.95 10.47 CEM 15

Ravena, NY 1 Wet 106.3 40% - Coal60% - Coke

4.9 9.38 CEM 15

Tulsa, OK 1 Dry 38.5 100% - Coal 4 7.5 CEM 15

Harleyville, SC 1 Preheater 85 100% - Coal 3.5 5.87 CEM 15

3. California Portland Cement Inc.

Rillito, AZ 1

2

3

Long Dry

Long Dry

Long Dry

17

17

17

71% - Coal28% - Gas1% - Coke

54.2% - Coal44.8% - Gas1% - Coke

66.8% - Coal31.8% - Gas1.2% - Coke

5

5

5

7.2 - 11.0(9.1)

7.2 - 11.0(9.1)

7.2 - 11.0(9.1)

EPA Method7E - CEMJun-91



16

16

16



(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


4 Precalciner 125 64% - Coal23.8% - Gas3.6% - Coke3.8% - Usedoil5.7% - Tires

3.4 3.6 - 6.6(5.1)

EPA Method7E - CEMJun-Aug-91

16

Mojave, CA 1 Precalciner 130 90.8% - Coal4.7% - Oil4.5% - Gas

3.1 3.9 CARB 100ComplianceTestMay-92

16

4. CBR Cement Corporation

Redding, CA 1 Preheater 85 80% - Coal20% - Tires

3.1 2.5 CEMJul-92

17

5. Holnam, Inc.

Theodore, AL 1 Precalciner 193.8 4 EPA Method7E9/24/91

18

Florence, CO 3 Wet 60 5.8 EPA Method7E10/24/91

18



(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


Fort Collins, CO 1 One-stagepreheater

61.7 8.1 CEMJan-Jun-92

18

Artesia, MS 1 Wet 62.5 12.5 CEM7/16/92

18

Clarksville, MO 1 Wet 170 6.8 CEM 18

Three Forks, MT 1 Wet 37.7 11.6 EPA Method 72/10/86

18

Ada, OK 1

2

Wet

Wet

40

40

15.9

19.5

KVB SystemJun-92

KVB SystemJun-92

18

Holly Hill, SC 1

2

Wet

Wet

60

102

5.7

5.3

CEM6/28/92

CEM7/9/92

18



(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


Morgan, UT 1

2

Wet

Wet

22

22

6.61

5.46

EPA Method7E 11/21/91

EPA Method7E11/27/91

18

18

Seattle, WA 1 Wet 56.2 8.12 EPA Method7E10/15/90

18

6. Lafarge Corporation

Demopolis, AL 1 Preheater 98 70% - Coal30% - WDFGas - Preheat

3.2 4.8 EPA Method7E9/5/8/91

19

Davenport, IA 1 Preheater-Precalciner

108.3 100% - Coal 3.2 217 lb/hr2.61

204.4 lb/hr2.07

EPA Method 79/21/82

6/6/84

20

20



(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


Fredonia, KS 1

2

Wet

Wet

17

28.5

100% - Coal

100% - Coal

5.98

6.17

5.85

~200 ppm4/11/89

~550 ppm9/17/91

~500 ppm9/18/91

EPA Method7E

21

21

21

Alpena, MI 1

2

Dry

Dry

70

45

78% - Coal22% - WDF

100% - Coal

5

4.6

957 ppm avg

393 ppm avg

CEM8/7/92

CEM8/7/92

22

22

Sugar Creek, MO 1 & 2 Dry 66.7 71.4% - Coal23.8% - Coke4.8% - Gas

4.52 6.1 EPA Method7E9/19/91

23

Paulding, OH 1 & 2 Wet 30 45.3% - Coal2.5% - Coke52.2% - WDF

5.3 3.6 EPA Method7E5/25/82

24



(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


Whitehall, PA 3 Four-stagepreheater

36 70% - Coal30% - Coke

90% - Coal10% - Tire



3.3 4.24

3.2

3.3

4.1

EPA Method7EDec-91

25

25

25

25

New Braunfels,TX

1 Preheater-Precalciner

122 50.2% - Coal40.7% - Coke9.1% - Gas

3 4.15 EPA Method7E3/90-5/90

26

7. Lehigh Portland Cement Co.

Leeds, AL 1 Preheater 83 89% - Coal11% - Gas

3.76 3.46 - Milloff2.24 - Millon

5/23/915/21/91

27

Cementon, NY 1 Wet 77 100% - Coal 5.25 5.9 5/22/90 27

Buda, TX 1 Precalciner 138 95% - Coal5% - Gas

3.63 3.8 6/30/86 27



(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


Waco, TX 1 Wet 10 68% - Gas32% - Coke

8.8 17.1 12/5/85 27

8. Lone Star Industries

Oglesby, IL 1 Dry 64.6 8

7.2

CEM5/92-6/92

EPA Method 712/13/83

28

28

Greencastle, IN 1 Wet 91.7 5 CEM 28

Cape Girardeau,MO

1

1

1

Precalciner

Precalciner

Precalciner

139.4

139.4

139.4

1.4(178 ppm)

0.9(115 ppm)

1.5(182 ppm)

CEM4/13/92

CEM4/15/92

CEM6/25/92

28

28

28

Sweetwater, TX 3 Preheater 20.8 11.68 EPA Method 7Apr-May 1991

28



(tons/hr)

Fuel burned Heat in

MM Btu/ton

NOX emissions

(lb/ton

clinker)

Method and

date of data

Reference


9. Southdown, Inc.

Brooksville, FL 1 Preheater 80 100% - Coal 3.2 3 CEMFeb-92

29

Fairborn, OH 1 Preheater 85 80% - Coal20% - LWDF

3.9 11 CEMDec-91

29

Knoxville, TN 1 Preheater-Precalciner

80 75% - Coal12% - LWDF13% - SWDF

3.6 7 CEMJan-91

29

47

The kilns with mid-kiln firing reported much greater NOX emissions ranging from 9 to 18.3

lb/ton of clinker, whereas other waste-fuel burning wet kilns reported much lower NOX

emissions ranging from 3.6 to 8.1 lb NOX/ton of clinker. NOX emissions data from these kilns

prior to introducing waste fuels, however, were not available to directly assess the effect of waste

fuel burning on NOX emissions.

The-long dry kilns consume significantly less energy than wet kilns (about 4.5 MM

Btu/ton on average) and produce less NOX emissions in the range of 6.1 to 10.5 lb NOX/ton of

clinker with an average of 8.6 lb NOX/ton of clinker. The wet and long dry kilns are similar in

terms of structure and firing of fuels. The difference in the NOX emission rates may thus be

attributed to the difference in the energy consumption rates in these two types of kilns.

The preheater kilns reported NOX, emissions in the range of 2.5 to 11.7 lb NOX/ton of

clinker with an average of 5.9 lb NOX/ton of clinker. The high values of 8.1 and 11.7 were

incidently found in gas burning kilns. As expected, the energy consumption of preheater kilns

was much lower, about 3.8 MM Btu/ton. In addition, combustion of a part of the fuel at a lower

preheating temperature is expected to reduce the NOX emissions as compared to burning all the

fuel in the hot kiln burning zone. These two factors account for the lower NOX emissions in

preheater kilns as compared to wet or long dry kilns.

The precalciner kilns produced the least NOX emissions ranging from 0.9 to 7.0 with an

average of 3.8 lb NOX/ton of clinker. These kilns are the most energy efficient with an average

energy consumption of 3.3 MM Btu/ton of clinker. Precalciner kilns have lower NOX emission

rates because they burn more fuel at the calcining temperature.

There have been many changes in the six years since the 1994 ACT document was

published. One of the most interesting from an emissions estimation perspective is the increased

use of continuous emissions monitors (CEM) on cement kilns. In January 2000, the PCA and

PCA provided results of a survey of cement facilities where the respondents indicated 46% of the

operating U.S. kilns (74 kilns) have already installed a CEMS (81% of the facilities representing

81% of the operating U.S. kilns responded to the survey). The remaining 87 kilns that are

represented by the survey have not installed a CEMS.30,31 CEMs record NOX measurements at

closely spaced intervals. These measurements are accumulated and averaged by a process

control computer at preset time intervals. CEMs data provide a better estimation of average NOX

emissions from cement kilns than do short-term tests because of the high degree of variability in

NOX emissions and autocorrelation between sequential NOX measurements.32

Eight state air pollution control agencies were asked to provide NOX emissions data for

their kilns. These data were supplemented with additional test data, and industry literature to

determine average uncontrolled emission rates for the four kiln types.33 These most recent data

are summarized in Table 4-3. The emissions data from the state agencies are primarily from

CEMS and are the reported annual emissions for the facilities. Most of the states did not report

production values (because they tend to be confidential) so kiln capacities5 were used to

48

determine emission rates. The kilns were also assumed to operate for an average of 8,000 hours

per year. In addition, most of the state agencies did not provide additional information on any

NOX control measures that may have been implemented (e.g., low-NOX burners). The resulting

average emission rates are generally lower than the average emission rates calculated in 1994 or

presented in AP-42. The lower numbers are probably a result of using kiln capacities rather than

actual kiln production values but may also be a result of assumptions regarding the installation of

NOX control devices (approximately 14% of the operating U.S. kilns have installed low-NOX

burners - see section 5.2.1.2).30,31

TABLE 4-3. SUMMARY OF ADDITIONAL NOX EMISSION DATA

FOR DIFFERENT KILN TYPES

Cement kiln

type

Average

rate (lb/ton

of clinker)

Range of

rates (lb/ton

of clinker)

Number of

Data Points

Wet kiln 6.2 1.9 - 13.4 10

Long dry kiln 4.5 2.5 - 7.1 6

Preheater kiln 1.7 0.4 - 3.7 6

Precalciner kiln 2.9 1.1 - 5.6 12

All of the literature and data gathered indicate substantial spread in the reported NOX

emissions with significant overlap for different kiln types. Table 4-4 compares the NOX emission

rates from the 1994 ACT document, AP-42, and the data recently collected from the State air

agencies. The four different cement kiln types, however, do appear to have different levels of

NOX emissions and different characteristics influencing NOX formation. As shown, the rates

calculated from the State data are generally lower that the values calculated during development

of the 1994 ACT document. The new data are not necessarily more representative than the 1994

ACT document data. The lower rates derived from the new data probably result from the

assumptions made regarding kiln production and level of NOX control. It should be noted that

the lower emission rates derived from the new data for preheater kilns relative to precalciner

kilns is contrary to expectation and could be due to the lack of data points for preheater kilns.

The AP-42 factors are also lower than the 1994 ACT document rates but are primarily based on

short term emission tests, which do not capture the inherent variability of kiln NOX emissions,

and the data are all over 10 years old. When one reviews the original data summarized in the

1994 ACT document, the maximum or minimum NOX emission rate for a specific kiln type is

about equally greater or less than the calculated average. Because the data used to calculate the

1994 ACT document NOX emission rates are newer, these average emission rates may be more

representative of modern kilns than the factors presented in AP-42.34

49

1. Nielsen, P.B., and O.L. Jepsen. An Overview of the Formation of SOX and NOX in

Various Pyroprocessing Systems. Presented at the IEEE Cement Industry Technical

Conference XXXII. Tarpon Springs, FL. May 22-24, 1990.

2. Zeldovich, J. The Oxidation of Nitrogen in Combustion and Explosions: Acta.

Physiochem. 21(4). 1946.

TABLE 4-4. COMPARISON OF EMISSION RATES

Kiln Type Emission Rate (lb NOX/ton clinker)

1994 ACT AP-42 New Data

Wet 9.7 7.4 6.2

Long dry 8.6 6.0 4.5

Preheater 5.9 4.8 1.7

Precalciner 3.8 4.2 2.9

The emission data compiled for the 1994 ACT document will be used in estimating

uncontrolled emissions from typical cement kilns because these data are newer and include more

CEMS data than the data used in AP-42; the NOX emission rates derived in AP-42 have a “D”

quality rating (based on number of tests and variability of emissions from the process); and the

data collected from the state agencies are less certain because of lack of production data. These

data are presented in Table 4-5. This table also includes the heat input requirement for the

different cement kiln types which indicates a good correlation with the NOX emission rates.

TABLE 4-5. NOX EMISSION FACTORS FOR DIFFERENT KILN TYPES

Cement kiln type

Heat input requirement

(MM Btu/ton of clinker)

Average NOX emission

rate (lb/ton of clinker)

Range of NOX emissions

(lb/ton of clinker)

Wet kiln 6.0 9.7 3.6-19.5

Long dry kiln 4.5 8.6 6.1-10.5

Preheater kiln 3.8 5.9 2.5-11.7

Precalciner kiln 3.3 3.8 0.9-7.0

4.4 REFERENCES

50

3. U.S. Environmental Protection Agency. Control Techniques for Nitrogen Oxide

Emissions From Stationary Sources. Publication AP-47. National Air Pollution Control

Administration. Washington D.C. 1970.

4. Shreve, R.N., and J.A. Brink, Jr. Chemical Process Industries. New York, NY. Fourth

Edition. McGraw Hill, Inc. 1977.


Information Summary. December 31, 1998. 1999.

6. Portland Cement Association. Website:

(http://www.portlandcement.org/env/enviro2.asp). Accessed on July 11, 2000.

7. Hilovsky, R.J. NOX Reductions in the Portland Cement Industry With Conversion to

Coal-Firing. Presented at the 1977 U.S. EPA Emission Inventory/Factor Workshop.

Raleigh, NC. September 13-15, 1977.

8. Gartner, E.M. Nitrogenous Emissions From Cement Kiln Feeds: Portland Cement

Association Interim Report on Project HM7140-4330. Skokie, IL. June 1983.

9. Payne, R., T. Akiyama, and J.G. Witkamp. Aspects of NOX Formation and Reduction in

Coal Fired Combustion Systems. International Flame Research Foundation. Report NOX

F37/a/10. Ijmuiden, Netherlands. 1981.

10. Penta Engineering Corporation. Report on NOX Formation and Variability in Portland

Cement Kiln Systems Potential Control Techniques and Their Feasibility and Cost

Effectiveness. 1999.

11. Johansen, V., A. Egelov, and A. Eirikson. Emission of NOX and SO2, From Cement

Clinker Burning Installations. Zement-KalkGips NOX 10. 1986.

12. Scheuer, A. Theoretische und betriebliche untersuchungen zur bildung und zum abbau

von stickstoffmonoxid in zementdrehofenanlagen. Schriftenreihe der Zementindustrie,

Heft 49. 1987.


Publication AP-42. Fifth Edition. Volume I - Stationary Point and Area Sources.

Research Triangle Park, NC. January 1995. pp. 11.6-1 - 11.6-26.

14. Letter and attachments from Sweeney, D.M., Ash Grove Cement Company, to Neuffer,

W.J., U.S. Environmental Protection Agency. August 25, 1992. Response to

questionnaire on NOX emissions data.

51

15. Letter and attachments from Willis, D.A., Blue Circle Cement, Inc., to Neuffer, W.J.,

U.S. Environmental Protection Agency. October 2, 1992. Response to questionnaire on

NOX emissions data.

16. Letter and attachments from Bennett, J., California Portland Cement Company, to

Neuffer, W.J., U.S. Environmental Protection Agency. November 17, 1992. Response to


17. Letter and attachments from Ellison, J.E., Calaveras Cement Company, to Neuffer, W.J.,

U.S. Environmental Protection Agency. August 31, 1992. Response to questionnaire on

NOX emissions data.

18. Letter and attachments from Hackett, H.P., Holnam, Inc., to Jordan, B.C., U.S.

Environmental Protection Agency. August 28, 1992. Response to questionnaire on NOX

emissions data.

19. Letter and attachments from Gandy, M., Lafarge Corporation, to Jordan, B.C., U.S.


emissions data.

20. Letter and attachments from Smith, M.G., Lafarge Corporation, to Jordan, B.C., U.S.


emissions data.

21. Letter and attachments from Smith, R.G., Lafarge Corporation, to Jordan, B.C., U.S.

Environmental Protection Agency. July 31, 1992. Response to questionnaire on NOX

emissions data.

22. Letter and attachments from Johns, T., Lafarge Corporation, to Jordan, B.C., U.S.


emissions data.

23. Letter and attachments from Wallace, W., Lafarge Corporation, to Jordan, B.C., U.S.


emissions data.

24. Letter and attachments from Collins, B., Lafarge Corporation, to Jordan, B.C., U.S.


emissions data.

25. Letter and attachments from Weiss, R., Lafarge Corporation, to Jordan, B.C., U.S.

Environmental Protection Agency. August, 1992. Response to questionnaire on NOX

emissions data.

52

26. Letter and attachments from Harris, M.D., Lafarge Corporation, to Jordan, B.C., U.S.

Environmental Protection Agency. September 1, 1992. Response to questionnaire on

NOX, emissions data.

27. Letter and attachments from Matz, T.L., Lehigh Portland Cement Company, to Neuffer,

W.J., U.S. Environmental Protection Agency. October 27, 1992. Response to


28. Letter and attachments from Johnson, R.M., Lone Star Industries, to Jordan, B.C., U.S.

Environmental Protection Agency. October 9, 1992. Response to questionnaire on NOX

emissions data.

29. Letter and attachments from Gill, A.S., Southdown, Inc., to Neuffer, W.J., U.S.

Environmental Protection Agency. December 3, 1992. Response to questionnaire on NOX

emissions data.



31. Letter from R. Battye and S. Edgerton, EC/R Incorporated, Chapel Hill, NC, to B.

Neuffer, USEPA, RTP, NC. Summary of February 4, 2000 conference call on PCA

Survey - Preliminary NOX Control Technology Questionnaire. February 11, 2000.

32. Walters Jr., L.J., et. al. “Time-Variability of NOX Emissions from Portland Cement

Kilns.” Environmental Science & Technology. Vol. 33, No. 5, 1999, pp. 700 - 704.

33. Memo from R. Battye and S. Walsh, EC/R Incorporated to D. Sanders, U.S. EPA,

Derivation and data supporting development of cement plant NOX emission rates.

September 15, 2000.

34. Strietman, F.L, T.B. Carter, and G.J. Hawkins. Regulation and Control of NOX Emission

from the Portland Cement Industry. Presented at the 1999 IEEE Gulf Coast Cement

Industry Conference. Charleston, SC. September 30 and October 1, 1999.

53

5.0 NOX CONTROL TECHNIQUES

As discussed in Chapter 4, nitrogen oxides (NOX) are formed by the oxidation of nitrogen

during the fuel combustion process. The formation of thermal NOX is a function of the flame

temperature, flame turbulence, the amount of nitrogen and oxygen available for the thermal

reaction, and the gas phase residence time at high temperature. To reduce the amount of thermal

NOX formed, one or more of these variables needs to be minimized. The formation of fuel and

feed NOX is not as well understood as the thermal NOX formation. In general, however, the

greater the concentration of nitrogen in the fuel and feed, the greater the fuel NOX emissions.

Therefore, reducing the amount of fuel and feed-bound nitrogen should reduce the contribution

of the fuel and feed NOX.

The typical NOX emissions from a cement plant depend upon the type of the cement kiln

as shown in Table 4-6. For any given type of kiln, the amount of NOX formed is directly related

to the amount of energy consumed in the cement-making process. Thus, measures that improve

the energy efficiency of this process should reduce NOX emissions in terms of lb of NOX/ton of

clinker. With the rising costs of energy and the very competitive cement market, greater

attention is being paid to increasing overall energy efficiency, such as through reduction of over-

burning of clinker and improvement in gas-solids heat transfer. Continuous emissions

monitoring of CO, NOX, and O2 provide an indication of kiln conditions and also provide inputs

for process control. Newer cement kiln designs are generally based on preheater/precalciner

systems which provide very efficient gas-solids contact and greater energy efficiency.

NOX control approaches applicable to the cement industry may be grouped in three

categories:

1. Process modifications where the emphasis is on increased energy efficiency and

productivity (section 5.1);

2. Combustion control approaches where the emphasis is on reducing NOX

formation (section 5.2); and

3. NOX reduction controls which remove the NOX formed in the combustion process

(section 5.3).

Section 5.4 provides a discussion of the technologies supporting the recent selection of

Best Available Techniques (BAT) for NOX control at European cement kilns. Section 5.5 gives a

summary of the applicable NOX control technologies, and section 5.6 provides the references for

this entire chapter.

54

5.1 PROCESS CONTROL MODIFICATION

Process modifications are applicable to any type of kiln and are usually done to reduce

heat consumption, to improve clinker quality, and to increase the lifetime of the equipment (such

as the refractory lining) by stabilizing process parameters. Reduction of emissions, such as NOX,

SOX, and dust, are secondary effects of these modifications. Smooth and stable kiln operation

close to design values for process parameters is beneficial for all kiln emissions. Process

modifications can include many elements, such as instruction and training of the kiln operators,

homogenizing raw material, ensuring uniform coal dosing, improving the cooler’s operation, and

installing new equipment. Process modifications are primarily done to reduce operating costs,

increase capacity, and improve product quality. Adopting process modifications usually results

in a reduction of operating costs for a kiln. The savings result from reduced fuel and refractory

consumption, lower maintenance costs, and higher productivity, among other factors.1

This section describes process modifications that improve fuel efficiency and kiln

operational stability with an emphasis on reducing NOX formation. Since NOX formation is

directly related to the amount of energy consumed in cement-making, improving fuel efficiency

and productivity will reduce NOX emissions.

5.1.1 Combustion Zone Control of Temperature and Excess Air

Continuous monitoring of O2 and CO emissions in the cement kiln exhaust gases

indicates the amount of excess air. At a given excess air level, NOX emissions increase as the

temperature of the combustion zone increases. A typical kiln combustion zone solids

temperature range is about 1430 to 1540 C (2600 to 2800 F) for completion of clinkering

reactions and to maintain the quality of the cement produced.2 The corresponding gas-phase

temperature is usually greater than 1700 C (3100 F).3 Maintaining the combustion zone

temperature at a necessary minimum value would minimize both the process energy requirement

and the NOX emissions.

Along with the appropriate temperature, it is also necessary to maintain an oxidizing

atmosphere in the clinker burning zone to ensure the quality of the clinker produced. Although a

kiln could be operated with as little as 0.5 percent kiln exhaust oxygen level, typically the kiln

operators strive for an oxygen level of 1 to 2 percent to guarantee the desired oxidizing

conditions in the kiln burning zone. An experimental test on a cement kiln showed that by

reducing excess air from 10 to 5 percent (i.e., reducing exhaust oxygen levels from 2 to 1

percent) NOX emissions per unit time can be reduced by approximately 15 percent.4,5

With state-of-the-art continuous emissions monitoring systems (CEMS) and feedback

control, excess air can be accurately controlled to maintain a level that promotes optimum

combustion and burning conditions in addition to lowering NOX emissions. Reducing excess air

level also results in increased productivity per unit amount of energy consumed and thus results

in an indirect reduction of NOX emissions per unit amount of clinker product.

55

5.1.2 Feed Mix Composition

Heat requirements for producing clinker are dependent on the composition of the raw

feed which varies among cement plants. Experiments have demonstrated that by improving the

burnability of the raw feed, the heat requirement of clinker can be reduced by 15 percent.6 If the

raw feed composition can be formulated to require less heat input per ton of clinker, less fuel is

burned and less NOX per unit product is produced. This approach of changing the feed

composition may, however, be highly site specific and may not be applicable at all locations.

5.1.2.1 Reduction of Alkali Content of Raw Feed

The alkali content of finished cement generally needs to be below a certain acceptable

level. Low alkali requirements need higher kiln temperatures and longer residence times at high

temperatures to volatilize the alkali present in the semi-molten clinker. Raw materials with

greater alkali content need to be burned longer at higher temperatures to meet alkali requirements

and thus may produce greater NOX emissions. Increased volatilization of alkali also results in

increased alkali emissions in kiln exhaust gases. To control alkali emissions, a part of the kiln

exhaust gases may be bypassed around a downstream unit, e.g., a precalciner. The bypassed

gases are quenched to remove alkali and sent through a particulate collector. The bypass of kiln

exhaust gases typically involves a fuel penalty, e.g., about 20,000 Btu/ton of clinker for every 1

percent gas bypass. The additional heat requirement may also contribute to increased NOX

emissions; thus, reducing the alkali content of the raw feed mix may contribute to a reduction in

the NOX emissions.

5.1.2.2 CemStar Process.

Another feed modification that can reduce NOX emissions is the addition of a small

amount of steel slag to the raw kiln feed. This patented technique is known as the CemStar

Process and was developed by TXI Industries. Steel slag has a low melting temperature and is

chemically very similar to clinker. Since many of the chemical reactions required to convert steel

slag to clinker have already taken place in a steel furnace, the fuel needed to convert steel slag

into clinker is low. The decreased need for limestone calcination per unit product and improved

thermal efficiency of the process both contribute to reduced thermal NOX and CO2 emissions.7

Eleven facilities are using or in the process of incorporating CemStar.8 CemStar requires

little extra equipment and the addition of steel slag to the feed mix can result in a reduction or

elimination of the need for some mineral sources, such as shale or clay. This process can also

increase production by 15 percent.7

According to the Entellect Environmental Services “Evaluation of the Effects of the

CemStar Process on a Wet Process Cement Kiln” report, the CemStar process reduces the kiln

material temperature in the region of the flame by an average of 200F (from 2610F to

2405F); the lower gas temperature of the flame results in lower NOX emissions.9 Another test

56

of CemStar technology found an average reduction in burn zone temperature of 160 F, a six

percent reduction.9 The amount of NOX emissions reductions achievable with CemStar varies by

kiln type but ranges from over 20 to 60 percent.7 Short- and long-term tests of CemStar were

conducted at two different types of TXI cement kilns in 1999. Short-term tests (two days) on a

preheater/precalciner kiln found NOX emissions reductions in lbs NOX /ton of clinker of 44

percent when operated at maximum capacity, and between 9 and 30 percent when operated at

normal capacity, depending on the quality of the raw feed mix (see Table 5-1).

TABLE 5-1. RESULTS OF SHORT-TERM CEMSTAR TESTS ON A

PREHEATER/PRECALCINER KILN

Poor Quality Feed

Mix

(lb NOX/ton of

clinker)

Percent

Reductiona

(%)

Ideal Quality

Feed Mix

(lb NOX/ton of

clinker)

Percent

Reductiona

(%)

Without CemStar 4.98 - 5.59 -

With CemStar at

normal feed rateb

4.51 9 3.89 30

With CemStar at

maximum feed ratec

(no test) - 3.15 44

aPercent reductions are relative to the emission rate without CemStar.

b The normal feed rate is 170 - 180 tons per hour of dry feed.c The maximum feed rate is 195 tons per hour of dry feed.

Andover Technologies also reported on short-term and long-term tests of a wet kiln using

CemStar Technology. The short-term tests (one day) found emission reductions of 36 to 55

percent in lbs NOX/ton of clinker, and the long-term tests (approximately two and a half months)

found reductions of 24 percent (see Table 5-2).7

Kilns with lower initial baseline NOX emissions would have less NOX reductions with

CemStar than those with higher baseline emissions. Wet and long-dry kilns would have greater

NOX reductions with CemStar because more energy is used per ton of clinker produced than

preheater/precalciner kilns. Wet kilns may achieve the greatest NOX reductions with CemStar

because the addition of steel slag would reduce the amount of water needed to create the slurry

and consequently decrease the amount of heat needed to dry it.7

57

TABLE 5-2. RESULTS OF CEMSTAR TESTS ON A WET KILN

Test 1

(lb NOX/ton of clinker)

Test 2


Percent

Reductiona (%)

Short-Term Test

Without CemStar 17.53 24.7 -

With CemStar 11.24 no 2nd test test 1 = 36

test 2 = 55

Long-Term Test

Without CemStar 5.23 no 2nd test -

With CemStar 4.00 no 2nd test 24aPercent reductions are relative to the emissions rate without CemStar during the same test period.

5.1.3 Kiln Fuel

Changing the primary kiln fuel from natural gas to coal can reduce the flame temperatures

significantly, resulting in lower thermal NOX emissions.10,11 Although nitrogen present in coal

may provide greater fuel NOX contribution, switching the fuel burned in kilns from natural gas to

coal has been shown to provide substantial reduction in the total NOX emissions in one

experimental study.10 In the dry process kilns tested in this study the average NOX emissions

decreased from 20.4 lb/ton of clinker to 6.2 lb/ton of clinker when the fuel was changed from

natural gas to coal. A number of cement kilns have already made the switch from natural gas to

coal and currently 87 percent of cement kilns in the United States use coal as the primary fuel.12

When natural gas (with no nitrogen in the fuel) is used in the burning zone of a cement

kiln, the NOX emissions are significantly higher than when coal is used. There may be additional

environmental impacts when coal is burned as opposed to natural gas (e.g., sulfur dioxide and

sulphate emissions may increase). Although switching to a lower nitrogen fuel in a precalciner

may reduce NOX, the fuel nitrogen content in the burning zone has little or no effect on NOX

generation. Some researchers have found no relationship between fuel nitrogen content and the

NOX emissions from a cement kiln.13

Switching to a fuel with a higher heating value and lower nitrogen content may reduce

NOX emissions in a cement kiln, e.g., petroleum coke has a lower nitrogen content per million

Btu than coal. Petroleum coke is also more uniform in terms of heat value, lower in volatile

matter content and burns with a lower flame temperature. However, petroleum coke cannot be

burned alone because it does not provide enough volatile matter.14

58

5.1.4 Increasing Thermal Efficiency

The thermal efficiency of the cement-making process may be increased by improving

gas/solids heat transfer, e.g., using an efficient chain system, increasing heat recovery from

clinker cooler, and by minimizing infiltration of cold ambient air leaking into the kiln. Heat

recovery from a clinker cooler may be improved by increasing the proportion of secondary air.

Recycling cement kiln dust from the dust collectors would reduce the energy requirement per ton

of a clinker. By increasing the thermal efficiency, NOX emissions are reduced per ton of clinker

produced.

5.2 COMBUSTION MODIFICATION

Combustion modifications are generally applicable to all types of kilns and are an

efficient way to reduce the formation of thermal NOX. The combustion modifications discussed

in this section focus on staging the combustion to minimize combustion at the maximum

temperatures. This can be accomplished by modifying the way oxygen or fuel is provided for

combustion.

5.2.1 Staged Combustion of Air

Staging of combustion air allows combustion of fuel to proceed in two distinct zones. In

the first zone, the initial combustion is conducted in a fuel-rich, oxygen-poor flame zone. This

zone provides the high temperatures necessary for completion of the clinkering reactions, but the

lack of available oxygen minimizes the formation of thermal and fuel NOX. The lack of

sufficient oxygen leads to only partial combustion of the fuel.

In the second, fuel-lean zone, additional (secondary) combustion air is added to complete

the combustion process. However, the temperature in this second zone is much lower than the

first zone because of mixing with the cooler secondary air, so the formation of NOX is minimized

in spite of the excess available oxygen. This staged approach can be used for combustion of all

fossil fuels. Staged combustion is typically achieved by using only a part of the combustion air

(primary air) for fuel injection in the flame zone, with remaining secondary air being injected in

the subsequent cooler zone.

For effective staging of combustion air to reduce NOX emissions, cement plants must

have indirect-fired kilns. In a direct-fired cement kiln, air used for conveying pulverized coal

from a coal mill, i.e., primary air, is typically 17 to 20 percent of the total combustion air. The

amount of primary air may be reduced by separating the coal mill air from coal. A cement kiln

using less than 10 percent of primary air is an indirect-fired kiln. Conversion of a direct-fired

kiln to an indirect-fired kiln involves adding particle separation equipment such as a cyclone or a

baghouse and a fan to provide the primary air used to transport the powdered coal from storage to

the kiln. An indirect-firing system increases overall energy efficiency by allowing a greater

proportion of hot clinker cooler air to be used as secondary combustion air.

59

5.2.1.1 Flue Gas Recirculation

In addition to changing the combustion air distribution, the oxygen content of the primary

air may be reduced to produce a fuel-rich combustion zone by recycling a portion of the flue gas

into the primary combustion zone.15 The recycled flue gas may be premixed with the primary

combustion air or may be injected directly into the flame zone. Direct injection allows more

precise control of the amount and location of the flue gas recirculation (FGR). In order for FGR

to reduce NOX formation, recycled flue gas must enter the flame zone. The FGR also reduces the

peak flame temperature by heating the inert combustion products contained in the recycled flue

gas.

The use of FGR may not be a viable method of reducing NOX in a full-size cement kiln

burning zone. FGR’s effectiveness relies on cooling the flame and generating an oxygen-

deficient (reducing) atmosphere for combustion to reduce NOX formation, conditions that may

not be compatible with cement kiln operation. High flame temperature and an oxidizing

atmosphere are process requirements to produce a quality clinker product. A cement kiln differs

from a utility boiler and other combustion devices because minimum temperatures and an

oxidizing atmosphere are required to initiate chemical reactions in a cement kiln in addition to

the providing the required heat (Btu/ton of clinker). Reduced flame temperatures and reducing

conditions in the burning zone of a cement kiln may not be compatible with the production of

cement clinker.13

Coupling a low-NOX step burner with flue gas recirculation has been shown to reduce

NOX emissions further in a cement kiln.16 The additional NOX reduction attributable to FGR was

estimated to be about 15 to 38 percent depending upon the proportion of FGR used.16

Incorporation of FGR in a cement

kiln also results in somewhat

increased power consumption and

reduced kiln output.

5.2.1.2 Low-NOX Burners

Some cement kiln burners,

specifically marketed as low-NOX,

burners, typically use 5 to 7 percent

primary air17,18 and thus can be used

only on indirect-fired kiln systems.

Low-NOX burners can be installed on

any type of kiln. Low-NOX burners

are designed to reduce flame

turbulence, delay fuel/air mixing, and

establish fuel-rich zones for initial

combustion. The longer, less intenseFigure 5-1. Schematic of low-NOX burner.17

60

flames resulting from the staged combustion lower flame temperatures and reduce thermal NOX

formation. Some of the burner designs produce a low pressure zone at the burner center by

injecting fuel at high velocities along the burner edges. Such a low pressure zone, as shown in

Figure 5-1,17 tends to recirculate hot combustion gas which is retrieved through an internal

reverse flow zone around the extension of the burner centerline. The recirculated combustion gas

is deficient in oxygen, thus producing a similar effect as FGR. Combustion of the fuel in the first

stage thus takes place in an oxygen-deficient zone before the fuel is diluted in the secondary air.

Installing such a burner reduces NOX emissions from the kiln-burning zone by up to 30

percent.17,19,20

Low-NOX burners have been used by the cement industry for twenty years.21 Many

suppliers offer low-NOX burners and most of these systems focus on lowering the NOX formation

in the calciner by air or fuel staging, by reburning, or by high temperature combustion.22 Test

data from several different low-NOX burners are now available. Thomsen, Jensen, and

Schomburg reported on tests of a F.L. Smidth in-line calciner low-NOX system in a

preheater/precalciner kiln where different percentages of coal were added to the reduction zone

of the precalciner (the remaining coal was added to the oxidizing zone).22 When 100 percent of

the coal was added to the reduction zone of the precalciner, the NOX content at the preheater exit

was reduced by 44 percent relative to when zero coal was added (see Table 5-3).

TABLE 5-3. NOX EMISSIONS FROM A PRECALCINER EQUIPPED

WITH A LOW-NOX BURNER

Percent Coal Added to

Reduction Zonea


NOX Emissionsb


Percent

Reductionb

(%)

0 2.8 -

50 1.9 31

100 1.6 44a

The remaining percentage of the coal was added to the oxidizing zone.b

Emission measurements were taken at the preheater exit.c

Percent reductions are relative to emissions when zero percent of the coal was added; the original measurements

were in kg NOX/ton of clinker to the hundredth place - the percent reductions were calculated using the original

measurements, which results in slightly different values than when lb NOX/ton of clinker are used.

Steinbiß, Bauer, and Breidenstein reported emissions changes for five kilns before and

after the installation of Pyro-Jet low-NOX burners (see Table 5-4).21 The emission reductions

ranged from 15 to 33 percent. Information on kiln-type was not provided.

61

TABLE 5-4. NOX EMISSIONS BEFORE AND AFTER INSTALLATION

OF PYRO-JET LOW-NOX BURNERS

Kiln Before Installation

(ppm)

After Installation

(ppm)

Percent Reduction

(%)

A 970 650 33

B not given not given 30

C 650 460 29

D 900 730 19

E not given not given 15

There are two new data sources on emissions reductions from the use of Rotaflam® low-

NOX burners. The Pillard Combustion Equipment and Control Systems published data on four

kilns, comparing NOX emissions with a 3 channel burner to emissions when a Rotaflam® burner

was used (see Table 5-5).23 The emission reductions ranged from 23 to 47 percent. Information

on kiln-type was not provided.

TABLE 5-5. NOX EMISSIONS WITH 3 CHANNEL AND ROTAFLAM®

LOW-NOX BURNERS

Kiln With 3 Channel

Burner (ppm)

With Rotaflam®

Burner (ppm)

Percent

Reduction (%)

A 774 409 47

B 865 664 23

C 484 350 28

D 487 336 31

Emissions data are also available before and after a Rotaflam® low-NOX burner was

installed on a long-wet kiln (see Table 5-6).24 The average emissions decreased 14 percent.

62

TABLE 5-6. EMISSIONS BEFORE AND AFTER INSTALLATION OF A

ROTAFLAM® BURNER ON A WET KILN

Year Average Emissions


Percent Reductiona

(%)

1990 277 -

1992b 288 -

1993 269 -

1994 275 -

1995

(Rotaflam® installed)

239 14

aPercent reduction is relative to the 1990, 1992-1994 average NOX emissions, 277.25 lb NOX/hr.

b1991 data were not provided.

The Fuller Company low NOX In-Line Calciner was installed in an RMC Lonestar kiln

which reported 30-40 percent reductions in the amount of thermally formed NOX after

installation.25

In January 2000, the PCA and PCA provided results of a survey of cement facilities

where the respondents indicated 14% of the operating U.S. kilns (22 kilns) have already installed

a low-NOX burner (81% of the facilities representing 81% of the operating U.S. kilns responded

to the survey). The remaining 139 kilns that are represented by the survey have not installed low-

NOX burners.26,27

5.2.2 Staged Combustion of Fuel

In conventional long (wet or dry) rotary kilns, all heat required for the cement-making

process is supplied in the primary kiln burning zone, where the combustion occurs at the hottest

temperature in the kiln. In the cement-making process, the preheating and calcination of the raw

materials requires a large amount of heat but are typically at a temperature of 600 to 900 C

(1100 to 1650 F) which is much lower than the kiln’s clinker-burning temperature of 1200 to

1480 C (2200 to 2700 F).28 In the secondary combustion method, part of the fuel is burned at a

much lower temperature in a secondary firing zone to complete the preheating and calcination of

the raw materials.

5.2.2.1 Preheater/Precalciner and Tire Derived Fuel

This concept of a secondary firing zone is the basis of the preheater/precalciner cement

kiln design. Almost all new cement kilns have a preheater/precalciner-type designs. In the

preheater kilns, the primary emphasis is on efficient heat recovery from kiln exhaust gases (see

63

Figure 5-2).29 However, up to 15 to 20 percent of the fuel may be fired in the riser duct in

preheater designs.29

Precalciner systems typically employ a tower of four-stage cyclones for efficient gas-

solids contact which improves the energy efficiency of the overall process (see Figure 5-3).29 In a

typical precalciner kiln almost 40 to 50 percent of the fuel is burned at a lower (calcination)

temperature which reduces the thermal NOX formation considerably.

Tire-derived fuel can also be added to the feed end of a preheater or precalciner kiln. The

Mitsubishi Cement Company’s Cushenbury Plant in Lucerne Valley, CA began using whole

waste tires as a fuel supplement in 1993. The waste tires are delivered in enclosed container

trucks and dumped into the plant’s automated handling system. A live bottom hopper and

singulator place the waste tires on a conveyor system. This conveyor system transports the tires

to the feed end of the kiln and drops the tire into an airlock system that allows the waste tire to

fall onto the feed plate inside the kiln at a rate of five to six tires per minute.

Currently, 8,000 to 9,000 tires are burned per day, totaling about 13 percent of the fuel.

Tires have a fuel content of approximately 14,000 Btu/lb and a sulfur content that is roughly the

same as the coal that would be used. The steel belting in the waste tires supplements the iron

requirements and approximately 2 percent of the iron in the final product comes from the tires.

Figure 5-2. Schematic of preheater.29 Figure 5-3. Schematic of precalciner.29

64

The addition of waste tires reduces NOX emissions from the kiln by 30 to 40 percent, and there is

no significant change in toxic, hydrocarbon, or metal emissions.30,31,32

5.2.2.2 Low-NOX Precalciners

Most of the major cement kiln suppliers are now offering “low NOX” precalciner designs

for new kilns. These designs typically inject a portion of the fuel into the feed end of the kiln,

countercurrent to the exhaust gas flow, as illustrated in Figure 5-4.33 This fuel is burned in a sub-

stoichiometric O2 environment to create a strongly reducing atmosphere (relatively high

concentrations of CO) by following the simplified reactions:

NO + C N + CO (5-1)

and

NO + CO N + CO2 (5-2)

This reducing atmosphere inhibits

the formation of fuel NOX and destroys a

portion of the NOX formed in the kiln

burning zone. In some designs, additional

fuel is then added, again with insufficient

O2 for complete combustion, to create

another reducing zone. Several precalciner

kilns in the US have recently been

retrofitted with these “low NOX”

precalciners and preliminary information

indicates a noticeable reduction in NOX per

ton of clinker.13 Up to 46 percent reduction

of NOX emissions have been reported

without causing excessive coating

difficulties in the kiln.33

As discussed in Section 4.2.2,

nitrogen present in the fuel may also

participate in the reduction of NOX. The

primary NOX formation mechanism in the

secondary firing is the fuel NOX formation

which depends upon the nitrogen content of the fuel used. In order for the above reactions (5-1)

and (5-2) to proceed at reasonable rates the temperature in the reduction zone should be

maintained between 1000 and 1200 C (1830 to 2190 F). These temperatures may lead to

coating difficulties, particularly if the fuel used is coal with high ash content.34

Figure 5-4. Reduction of NOX emissions from

precalcining kiln system by fuel injection in the

rotary kiln gas outlet.33

65

It is not possible to use “staged combustion” on preheater kilns that are firing fuel in the

riser since in staged combustion it is necessary to add the fuel in an oxygen deficient atmosphere

and then supply additional combustion air to fully combust the fuel. Preheater kilns do not have

tertiary air ducts to supply the additional combustion air. The air for combustion of the

secondary fuel must come through the kiln, which precludes introducing the secondary fuel into

an atmosphere with insufficient oxygen for complete combustion.13

Emissions reductions have also been found when tire derived fuel was burned in a

precalciner. In one case, when 47 percent of the coal fired in the calciner was substituted with

tire-derived-fuel, a reduction in NOX emissions of about 29 percent was observed.35

5.2.2.3 Mid-Kiln Firing

The concept of staged combustion of fuels may also be used in conventional wet and

long-dry kilns by injecting solid fuel into the calcining zone of a rotating long kiln using a

specially designed feed injection mechanism.36 This system is known as mid-kiln firing (MKF)

and allows part of the fuel to be burned at a material calcination temperature of 600 to 900 C

(1100 to 1650 F) which is much lower than the clinker burning temperature of 1200 to 1480 C

(2200 to 2700 F).28

To maintain a

continuity in the heat input,

solid and slow burning fuels

(such as tires) are most

amenable for MKF. The

Cadence feed fork MKF

technology was first

introduced in 1989. It can be

installed during an annual

maintenance shutdown. It is

comprised of three primary

components: (1) a staging arm

or ‘feed fork’ that picks up the

fuel modules and positions

them for entry into the kiln, (2) two pivoting doors that open to allow the fuel modules to drop

into the kiln, and (3) a drop tube that extends through the side wall of the kiln. In addition to

these basic components, feed fork technology also requires a delivery system which positions the

fuel models so they can be picked up by the feed fork and a mechanism for opening the doors so

the fuel modules can enter the kiln.37 Due to the rotation of the kiln, fuel can be conveniently

injected only once per revolution from the top, as shown in Figures 5-529 and 5-6.38

Although most feed forks today are dedicated to whole tires, one facility uses baled

industrial waste as a fuel, and many others are investigating a variety of energy containing waste

Figure 5-5. Schematic of mid-kiln firing.29

66

materials from carpet scrap to pharmaceutical waste. These energy-bearing waste materials can

be containerized or dementionalized into discrete fuel modules to be fed to the kiln using the feed

fork.37

Inserting whole tires into mid-kiln locations can

give precalciner stability to the kiln. The operators have

two points of control to assist in stabilizing kiln

operation. Tires burn for 15 to 20 minutes within the

kiln after entry. This is deduced from observations of

the rate of change in kiln exit oxygen levels after entry

of tires begins. With proper instrumentation, control of

the kiln can be improved by adding solid fuels mid-

kiln.39

Mid-kiln firing of tires or other waste-derived

fuels does not reduce the final product quality; in fact,

many of Cadence’s cement kiln partners have reported

an improvement in the clinker burnability and mineralogy. The enhanced control has shown to

impart better formation of clinker. Reductions in cement fineness have been shown while

maintaining similar seven-day strengths. Several facilities also have reported an extended life of

the refractory in the burn zone.37,39

By adding fuel in the main flame at mid-kiln, MKF changes both the flame temperature

and flame length. These changes may reduce thermal NOX formation by burning part of the fuel

at a lower temperature and by creating reducing conditions at the solid waste injection point

which may destroy some of the NOX formed upstream in the kiln burning zone. MKF may also

produce additional fuel NOX depending upon the nitrogen content of the fuel.38 However, as

discussed in section 5.1.3, fuel NOX is unimportant relative to thermal NOX formation.

Additionally the discontinuous fuel feed from MFK can result in increased CO emissions

especially if hazardous wastes are used. To control CO emissions, the kiln may have to have

increased combustion air which can decrease production capacity.40

According to literature from Cadence, in tests of its feed fork technology, one kiln

reduced NOX emissions by 38%, overall particulate emissions by 14%, metal emissions by 30%,

SO2 emissions by 36%, and net emissions of all hydrocarbons by 29%.37,39 In the research

conducted for this report, test data were compiled for seven dry kilns and three wet kilns with

MKF technology. In nine tests on the dry kilns, the average reduction in NOX emissions was

33%, with a range from 11% to 55%. In three tests on the wet kilns, the average reduction in

NOX emissions 40%, with a range from 28% to 59% (see Table 5-7).40,41,42,43,44 It should be noted

that the three kilns that are known to have CEMS all reported emissions reductions of 45 percent

or more.

Figure 5-6. Schematic of fuel

injection in kiln.38

67

TABLE 5-7. EMISSIONS FROM KILNS WITH MID-KILN FIRING

Emissions


Percent

Reduction (%)

Emissions Based on

CEMS Data

Dry Kilnsa

A40 not given 13.6 unknown

B40 not given 11.1 unknown

C24, 44 not given 45.1 yes

C40 not given 55.3 yes

D21, 41 2.7 not given unknown

E22, 42 10.2 13.9 unknown

F40 not given 46.6 unknown



Average

(Dry Kilns)

6.4 33.3

Wet Kilns

G23, 43 not given 59.0 yes

H40 not given 35.0 unknown

I40 not given 27.6 unknown

Average

(Wet Kilns)

n/a 40.5

Average

(Dry & Wet Kilns)

6.4 35.1

aThere was more than one test at some kilns.

Waste-derived fuels with high heating values represent an economical source of energy

for the cement industry and its consumption has been increasing during the past decade.12 Mid-

kiln firing is a proven technology and so far at least 21 long kilns in the U.S. and nearly 40 kilns

worldwide have been modified to allow mid-kiln firing of solid and hazardous waste.37, 45

5.3 NOX REMOVAL CONTROLS

NOX removal controls are intended to destroy NOX that is formed in the combustion

process. Selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) are

described; however, SCR has not been demonstrated on any cement kilns in the United States at

68

this time. There have been two demonstrations of SNCR in the United States and there are 18

actual full-scale installations of SNCR for cement kilns in Europe. Biosolids injection

technology is not technically SNCR, but the chemistry and the principles of its operation are

similar. For this reason it is discussed with the other NOX removal controls.

5.3.1 Selective Catalytic Reduction (SCR)

SCR is a process that uses ammonia in the presence of a catalyst to selectively reduce

NOX emissions from exhaust gases. This technology is widely used for NOX abatement in other

industries, such as coal-fired power stations and waste incinerators. The SCR process has been

used extensively in Japan to achieve a 90 percent reduction in NOX emissions from fossil fuel-

fired boilers.46 In the United States SCR technology has successfully been used for gas turbines,

internal combustion engines, and utility boilers.46

In SCR, anhydrous ammonia, usually diluted with air or steam, is injected through a grid

system into hot flue gases which are then passed through a catalyst bed to carry out NOX

reduction reactions. The two principal reactions are:

4 NH3 + 4 NO + O2 4 N2 + 6 H2O (5-3)

and

4 NH3 + 2 NO2 + O2 3 N2 + 6 H2O (5-4)

Equation (5-3) represents the predominant reaction since 90 to 95 percent of NOX

emissions in the flue gas are in the form of NO. A number of materials have been used for

catalysts. Titanium dioxide (TiO2) and vanadium pentoxide (V2O5) mixtures are most commonly

used as catalysts due to their resistance to SOX poisoning.47,48 Zeolite-based catalyst materials

have also been developed capable of operating at higher temperatures than conventional metal

based catalysts.48 The catalyst is typically supported on ceramic materials, e.g., alumina in a

honeycomb monolithic form. The active ingredients of the base metal (titania-vanadia) and

zeolite catalysts often make up the bulk of the substrate material. The catalyst shape and reactor

design vary depending upon the manufacturer. The optimum temperature for the catalytic

reactions depends upon the specific catalyst used and is usually 300 to 450 C (570 to 840 F).

This temperature may be higher than typical cement kiln flue gas temperatures, especially in

plants using heat recovery systems or baghouses for particulate collection. But it may be possible

to reheat the exhaust using heat recovery systems.

Ammonia is typically injected to produce a NH3:NOX molar ratio of 1.05-1.1:1 to achieve

NOX conversion of 80 to 90 percent with an ammonia "slip" of about 10 ppm of unreacted

ammonia in the gases leaving the reactor.49 The NOX destruction efficiency depends upon the

temperature, NH3:NOX molar ratio, and the flue gas residence time (or the space velocity) used

69

in the catalyst bed. The SCR reactor system can be designed for a desired NOX reduction using

appropriate reagent ratio, catalyst bed volume, and operating conditions.

In general, the catalysts may be fouled or deactivated by the particulates present in the

flue gas. In the case of cement plants, the presence of alkalies and lime as well as sulfur dioxide

in the exhaust gases is also of concern. Because of fouling problems, the SCR system must be

installed after the particulate collection device. Recent developments have led to sulfur tolerant

SCR catalysts which limit SO2 oxidation to less than 1 percent.50 Soot blowers may be used to

prevent dust accumulation on SCR catalysts.

In the cement industry, basically two SCR systems are being considered: low dust exhaust

gas and high dust exhaust gas treatment. Low dust exhaust gas systems require reheating of the

exhaust gases after dedusting, resulting in additional cost. High dust systems are considered

preferable for technical and economical reasons.1 Up to now SCR has only been tested on

preheater and semi-dry kiln systems, but it might be applicable to other kiln systems as well.1

Pilot plant trials on small portions (three percent) of the exhaust gas have shown

promising results in Austria, Germany, Italy, and Sweden. There are at least three suppliers in

Europe that offer full scale SCR to the cement industry with performance levels of 100 to 200

mg/m3 (approximately 0.2 to 0.4 lb/ton of clinker).1 A full-scale SCR demonstration plant is

being built in Germany with governmental financial support; a full-scale SCR plant is also under

consideration in Austria.1

There are currently no installations of SCR units in any United States cement plants. In

1976, Hitachi Zosen, an SCR manufacturer, conducted three pilot test programs to evaluate SCR

on cement kilns.3 During these tests, two suspension preheater kilns and a wet process kiln were

tested for 5,400 hours each. Electrostatic precipitators were used to remove particulates before

the flue gas entered the SCR unit. Also, a heat recovery system equipped with supplemental fuel

firing was provided to raise the flue gas temperatures to the required reaction temperatures.

Slipstreams of about 3,000 scfm were treated with initial NOX removal efficiencies of 98 percent.

However, after 5,400 hours of operation, NOX removal efficiencies dropped to about 75 percent

due to catalyst coating.

Full-scale production runs will have to be carried out in order to remove the technical

and economic uncertainties related to upscaling of the SCR technique. The main uncertainties

are related to the high dust concentration in the gases (up to 500 g/Nm3, approximately 1.0 lb/ton

of clinker), the catalyst dust removal techniques, lifetime of catalysts, and total investment costs.1

Feasibility studies have been carried out in Austria, Germany, the Netherlands, and Sweden. The

estimated costs vary considerably, with the production costs and lifetime of the catalyst being

major variables.1 Based on the experience in other industries, NOX reductions in the range of 80

to 90 percent are considered possible, regardless of kiln type.46 However, further studies are

needed to demonstrate the specific NOX reduction in the cement kiln exhaust gas environment.

70

5.3.2 Selective Noncatalytic Reduction (SNCR)

This control technique relies on the reduction of NOX in exhaust gases by ammonia or

urea, without using any catalyst, with the same reactions (5-3) and (5-4) as in the case of the SCR

process. This approach avoids the problems related to catalyst fouling, as in SCR technology,

but requires injection of the reagents in the kiln at a temperature between 870 to 1090 C (1600

to 2000 F). At these temperatures urea decomposes to produce ammonia which is responsible

for NOX reduction. In principle, any of a number of nitrogen compounds may be used, e.g.,

cyanuric acid, pyridine, and ammonium acetate. However, for reasons of cost, safety, simplicity,

and by-product formation, ammonia and urea have been used in most of the SNCR applications.

Because no catalyst is used to increase the reaction rate, the temperature window is

critical for conducting this reaction. At higher temperatures, the rate of a competing reaction for

the direct oxidation of ammonia which actually forms NOX becomes significant. At lower

temperatures, the rates of NOX reduction reactions become too slow resulting in too much

unreacted ammonia slip. The effective temperature window range can be lowered to about

700 C (1300 F) by the addition of hydrogen along with the reducing agent.51 Nalco Fuel Tech,

the producer of the SNCR technology NOXOUT®, has also introduced NOXOUT® PLUS which is

said to broaden the operating temperature window and to reduce ammonia slip and CO and NO2

formation.

In a conventional long kiln the appropriate temperature window is in the middle of a kiln.

Because of the rotating nature of a long kiln, continuous injection of ammonia- or urea-based

reagents is presently not possible. The technology developed for mid-kiln firing of containerized

solid fuels allows injection of a certain amount of material once during the kiln revolution.

Injection of solid ammonium or urea salts in this manner has not been used because of the rapid

decomposition of such salts. Therefore, SNCR technology has not been applicable for long dry

or wet kilns. However, Fuel Tech Inc. is currently evaluating dry dust or pellet injection methods

for direct injection into kilns.52

In preheater/precalciner type cement kilns, the temperatures at the cooler end of the

rotating kiln, in the riser duct, and in the lower section of the cyclone preheater tower are likely

to be in the temperature window appropriate for SNCR. Such kilns are therefore good candidates

for application of SNCR technology.

The NOX reduction efficiency of SNCR depends upon the temperature, residence time, as

well as ammonia and NOX concentrations in the flue gas. Injection of ammonia at a NH3:3NOX

proportion of 1 to 1.5 will reduce NOX emissions between 60 to 80 percent. Using a molar ratio

of 0.5 will give NOX reductions of approximately 40 percent.47 The reagent consumption can be

significantly higher with greater ammonia slip in SNCR systems as compared to SCR systems.

Operating experience has identified several concerns with both ammonia and urea-based SNCR

processes. The most frequently reported is the buildup of ammonium bisulfite scale which is

significant for sulfur-containing fuels. SNCR processes also appear to convert some NO to

71

N2O.53 The rate of N2O formation is a weak function of both the reactant and the NO

concentration. However, N2O formation seems to be inherently more prevalent in systems using

urea than those using ammonia.54

The NOX destruction efficiency also depends upon the flue gas residence time in the

appropriate temperature window. Unlike an SCR system where the reaction temperature is

controlled in a dedicated reactor, an SNCR system relies on the existing gas temperature profile

to provide an adequate residence time for a desired NOX destruction. Maximum achievable NOX

reduction in a cement kiln may thus depend upon the gas temperature profile.

The SNCR process was demonstrated in Europe in a preheater type kiln. Both ammonia-

and urea-based reagents were investigated. The reagents were injected in the bottom gas duct as

shown in Figure 5-7.55 With a molar ratio of reagent to

NO2 of 1:1, about 70 percent reduction in NOX emissions

was observed with ammonia-based reagent and about 35

percent NOX reduction was obtained with urea.55 With

this reagent ratio, there was no major increase in

ammonia emissions in exhaust gases over the

background level of ammonia emissions generated by

kiln feed material. Greater NOX reductions were

observed with more than stoichiometric amount of

reagent, although there was increasing ammonia 'slip' in

the exhaust gases.

Scheuer,of the Research Institute of the Cement

Industry in Dusseldorf, Germany, reported on 148 SNCR

trials carried out on five different kilns. Three kiln

systems had cyclone preheaters and two had grate

preheaters. A 25% molar concentration of NH3 in water

was the main reagent tested, with some additional testing

done with ammonium sulfate solutions and with urea

solutions. Scheuer reported that NO reductions with the

NH3/water solution ranged from 15% to 75% and that

temperature appeared to be one of the main determinants

of the effectiveness of the reagent. Maximum NO

reduction occurred at 980 C (1796F). NH3 escape occurred when temperatures were less than

900 C (1652F) and when the NO concentration fluctuated. NH3 utilization decreased

significantly with increasing NH3:NO molar ratio and with decreasing NO concentration in the

exhaust gases, indicating that SNCR appears to be less promising at low NO emissions rates.13,56

SNCR is presently being used in 18 cement kilns in Europe. Fifteen kilns are in

Germany, two are in Sweden, and one is in Switzerland. These kilns are either suspension

preheater kilns or precalciner kilns. The most common reagent used is 25% ammonia water.1

Figure 5-7. Application of SNCR in

preheater kiln.

72

NOX reduction rates vary from 10 to 50 percent with NH3/NO2 molar ratio of 0.5 to 0.9, NOX

emissions at these reductions are 2.4 to 3.8 lb/ton of clinker. Two dry process cyclone

preheater/precalciner kilns in Sweden achieve 80 to 85 percent reduction (1.0 lb/ton of clinker) at

a NH3/NO2 molar ratio of 1.0 to 1.1.1

F. L. Smidth and Company tested SNCR on a preheater/precalciner kiln.3 Ammonia was

injected into the lower cyclone of the preheater tower where temperatures are favorable for the

reduction reactions to occur. NOX emissions reductions during this experiment averaged 40

percent, but NOX reductions of over 90 percent were obtained when the ammonia injection rate

was 10 to 20 percent in excess of stoichiometric.

In the United States, SNCR has been tested on two kilns. NOXOUT® technology was

tested under ten different operating conditions at a preheater/precalciner kiln in Seattle,

Washington during October 1993. NOX emissions were effectively reduced from 3.5 to 6.0 lb

NOX/ton of clinker to less than 1 lb NOX/ton of clinker.57, 58 Another test of NOXOUT®

technology was conducted during October 1998 in Davenport, Iowa. This test found NOX

reductions of 10 to 20 percent from a baseline of approximately 350 pounds NOX/hour, although

higher levels of reduction are thought to be achievable when the baseline is higher.59 An

evaluation of NOXOUT® technology was conducted in 1994 for a long dry kiln in Southern

California, but the study concluded that application of the NOXOUT® technology at the subject

kiln was technically infeasible.60

5.3.2.1 Biosolids Injection (BSI)

The Mitsubishi Cement Corporation’s Cushenbury plant in Lucerne Valley, CA, uses

biosolids injection technology (BSI) to achieve SNCR of NOX. The BSI process was developed

by the Cement Industry Environmental Consortium (CIEC). The founding participants in the

CIEC are Southdown, Inc., Riverside Cement Company, Mitsubishi Cement Corporation,

California Department of Commerce (now Trade & Commerce Agency), and the San Bernardino

County Air Pollution Control District (now Mojave Desert Air Quality Management District).

This technology is covered under U.S. Patent No. 5,586,510 issued December 24, 1996.13

The basic principle is to utilize the naturally occurring ammonia content of dewatered

biosolids as the reagent. The dewatered biosolids are obtained from wastewater treatment plants.

Since the biosolids are mechanically dewatered without heat input, the solids content varies

between 16 and 30 percent (moisture content of 84 to 70%). Depending on the moisture content,

the net Btu content (after evaporating the moisture) of the biosolids varies between -750 and

+2200 Btu/lb. Since the biosolids heating value is relatively small, the net effect on kiln fuel

combustion is expected to be small.61

The same conditions that affect NOX reduction performance in SNCR affect BSI

performance: temperature (927C / 1700 F is optimal), residence time (> 0.5 seconds is

desirable), inlet NOX concentration, inlet CO concentration, and NH3/NOX molar ratio. Another

73

key issue is mixing effectiveness, which affects the extent of contact and, hence, reaction

between NH3 and NOX. The BSI technology is applicable to preheater/precalciner kilns because

the temperature window for BSI (927C / 1700 F) occurs in a location where it is feasible to

inject biosolids.61

The biosolids are injected into the mixing chamber where the flue gas stream leaving the

kiln and precalciner mix. The mixing chamber offers the benefits of good residence time in the

appropriate temperature window (927C / 1700 F) and high mixing effectiveness.61

At the Cushenbury plant, BSI underwent long-term testing and eventual adoption in 1994

and 1995. The kiln is fueled with coal (85 percent) and tires (15 percent). The plant began

using tire-derived fuel (TDF) in mid-1993, so it is difficult to isolate the effects of TDF or BSI on

NOX emissions. The company estimates that the use of TDF reduces NOX emissions from the

kiln by 30 to 40 percent.62 Before the SNCR technology was adopted, the company estimated

NOX emissions averaged 2.4 pounds/ton of clinker; afterwards, the average fell to 1.2 lb/ton of

clinker, a 50 percent reduction. The effects of BSI on CO emissions varies between a large

increase and no change at all, but in all cases it has remained below 500 ppm. BSI has not

caused any significant changes in either metal HAP or organic HAP emissions. Using the SNCR

biosolids technology, the kiln also reduced its fuel consumption by 5 percent.61

5.3.2.2 NOXOUT®

An SNCR process using aqueous urea was developed by Electric Power Research

Institute (EPRI) and is now marketed by Nalco Fuel Tech, Inc., under the trade name of

NOXOUT®. In the urea reaction with NO, one mole of urea reacts with two moles of NO to

complete the reaction to nitrogen, carbon dioxide and water. Normalized Stoichiometric Ratio

(NSR) is used to express the reagent feed rate relative to the reaction stoichiometry. The NSR

takes into account the 2:1 mole ratio of the NO:urea reaction as the “normalized” ratio. If 50%

of the urea reacts to reduce NO to nitrogen, reduction of 100% NOX occurs at NSR=2; 80%

reduction at NSR=1.6; 50% reduction at NSR=1.0, etc. Performance improves with increased

turbulence or mixing, residence time, and more favorable temperature conditions. A higher NOX

baseline generally leads to a higher percentage of NOX reduction.52

Urea is safer to handle than anhydrous ammonia. Both ammonia and urea need to be

injected in a similar temperature window which is 870 to 1090 C (1600 to 2000 F).

Proprietary additives have been developed by Nalco to widen the temperature window.63 One

modification of the urea-based SNCR system is the addition of methanol injection downstream

of the urea injection point to improve overall NOX removal. Nalco also introduced an improved

NOXOUT® PLUS, which is said to further broaden the operating temperature window and to

reduce ammonia slip and CO and NO2 formation.

The Ash Grove plant in Seattle is a preheater/precalciner kiln with average processing

rates of 160 tons dry feed/hour producing approximately 100 tons clinker/hour. NOXOUT® was

74

tested on this kiln under varying conditions, including the use of different fuel types (natural gas

and coal), heat input to the calciner (5 to 9 percent), and preheater O2 (1.8 to 2.9 percent). The

baseline NOX levels varied from 350 to550 lbs NOX/hour. When NOXOUT® was used, NOX

emission reductions varied significantly depending on the conditions, with a maximum reduction

of 90 percent (less than 100 lbs NOX/hour). Typical reductions were greater than 50%.58

NOXOUT® was tested for one week in October of 1998 on the preheater/precalciner kiln

at the Lafarge-Davenport Plant. Operating conditions were unstable most of that week and only

five hours of testing produced results that could provide a reasonable indication of what may be

achievable with NOXOUT®. The baseline NOX rate was approximately 350 lbs NOX/hour. Using

NOXOUT®, emission reductions of 10 to 20 percent were achieved.59 Operating conditions such

as residence time, temperature, and the use of coal at this kiln were contrasted to conditions at

the Ash Grove kiln that achieved greater reductions to explain why NOXOUT® may achieve

better results on some kilns than others.

Nalco also has conducted a number of demonstrations and commercial projects in

preheater/precalciner cement kilns. The fuels have included coal, and coal in combination with

No. 6 heavy fuel oil, waste oil, and/or tire chips. The clinker capacity on these kilns ranged from

approximately 1000 metric tons to 3200 metric tons per day. The results of two tests with

average NOX reductions of approximately 50%, were featured in a recent report (see Table 5-

8).52

TABLE 5-8. EMISSION REDUCTIONS FROM TWO KILNS USING NOXOUT®

Baseline NOX

Emissions

(ppm)

NOX Emissions

with NOXOUT®

(ppm)

Percent

Reduction

(%)

Kiln A, Test 1 412 203 51

Kiln A, Test 2 389 185 53

Kiln B 525 284 46

5.4 SUMMARY OF EUROPEAN EXPERIENCES

In Europe, many cement plants have adopted general primary measures, such as process

control optimization, use of modern, gravimetric solid fuel feed systems, optimized cooler

connections and use of power management systems. These measures are usually taken to

improve clinker quality and lower production costs but they also reduce the energy use and air

emissions.1

75

In March 2000, the European Integrated Pollution Prevention and Control (IPPC) Bureau

issued a report on Best Available Techniques for European cement kilns.1 The report collected

emissions data from several sources. Emission rates for European kilns included in this study

range from less than 0.8 to 12 lb NOX/ton of clinker. A set of German kiln emission

measurements presented in the European report found NOX emissions for a cyclone preheater

with heat recovery of 1.2 to 6.2 lb/ton of clinker, for a cyclone preheater without heat recovery of

1.6 to 7.0 lb/ton of clinker, and for a grate preheater of 1.6 to 8.2 lb /ton of clinker. These rates

are similar to the averages for preheater and precalciner kilns found by EC/R in the new data

presented in Chapter 4 (1.7 and 2.7 lb/ton of clinker respectively), but are less than those reported

in the ACT document (5.9 and 3.8 lb/ton of clinker respectively).1

Table 5-9 presents a summary of NOX control device applicability, reduction efficiency,

and reported average emissions from the IPPC Bureau report on BAT for European cement

kilns.1 There are no emissions data in the IPPC report for kilns with CemStar technology or mid-

kiln firing. For low-NOX burners, the IPPC report found a lower average NOX emissions rate

(1.6 lb/ton of clinker) than EC/R found in the new State data (8.98 lb/ton of clinker). Both the

IPPC report and the 1994 ACT document had estimated reduction efficiencies for low-NOX

burners of up to 30 percent. The reduction efficiencies in the IPPC report for SNCR (10 to 85

percent) and SCR (85 to 95 percent) are close to but slightly greater than those reported in the

1994 ACT document (30 to 70 percent and 80 to 90 percent respectively).

TABLE 5-9. NOX CONTROL TECHNIQUES SUMMARY FROM EUROPEAN

BEST AVAILABLE TECHNIQUES REPORT1

Technique Kiln Systems

Applicability

Reduction

Efficiency

Reported Emissions

mg/Nm3 a kg/tonne b

(lb/ton)

Flame cooling All 0 to 50% 400 0.8

(1.6)Low-NOX

burner

All 0 to 30%

Staged

combustion

Preheater and

Precalciner

10 to 50 % <500 to 1000 < 1.0 to 2.0

(2.0 to 4.0)

Mid-kiln firing Wet and long dry 20 to 40% no info no info

SNCR Preheater and

Precalciner

10 to 85% 200 to 800 0.4 to 1.6

(0.8 to 3.2)

SCR - data from

pilot plants only

Possibly all 85 to 95% 100 to 200 0.2 to 0.4

(0.4 to 0.8)a Normally referring to daily averages, dry gas, 273 K, 101.3 kPa and 10% O2.b kg/tonne clinker is based on 2000 m3/tonne of clinker.

76

The IPPC report concludes that BAT for reducing NOX emissions are a combination of

general primary measures, primary measures to control NOX emissions, staged combustion and

SNCR. The BAT emission level associated with the use of these techniques is 0.4 to 1.0 lb/ton

of clinker (200-500 mg NOX/m3 (as NO2) ). This emission level could be seen in context of the

current reported emission range of 0.4 to 6.0 lb/ton of clinker (<200-3000 mg NOX/m3), and that

the majority of kilns in the European Union is said to be able to achieve less than 2.4 lb/ton of

clinker (1200 mg/m3) with primary measures.1

While there was support for the above concluded BAT to control NOX emissions, there

was an opposing view that the BAT emission level associated with the use of these techniques is

1.0 to 1.6 lb/ton of clinker (500-800 mg NOX/m3 (as NO2)). There was also a view that selective

catalytic reduction is BAT with an associated emission level of 0.2 to 0.4 lb/ton of clinker (100-

200 mg NOX/m3 (as NO2)).1

5.5 SUMMARY OF APPLICABLE NOX CONTROL TECHNOLOGIES

Table 5-10 presents NOX control techniques and the types of kilns on which they are

applicable.

TABLE 5-10. NOX CONTROL TECHNIQUES AND

APPLICABLE TYPES OF CEMENT KILNS

NOX Control Technique

Applicable Kiln Type

Wet Long-Dry Preheater Precalciner

Process Control Systems yes yes yes yes

CemStar yes yes yes yes

Low-NOX Burnera yes yes yes yes

Mid-Kiln Firing yes yes no no

Tire Derived Fuelb yes yes yes yes

SNCR no no yes yesa Low-NOX burners can only be used on kilns that have indirect firing.b Tire derived fuel can be introduced mid-kiln in a wet or long-dry kiln, or at the feed end of a

preheater or precalciner kiln.

Table 5-11 presents a comparison between the NOX reductions identified in the 1994

ACT document and updated emissions data for various control technologies.

77

TABLE 5-11. COMPARISON OF 1994 ACT NOX EMISSIONS REDUCTIONS

WITH NEWLY AVAILABLE EMISSIONS DATA

1994 ACT64 Updated Emissions Data65

Possible

NOX

Emission

Reduction

(%)

Average

Emission

Reduction

(%)a

Range of

Emission

Reductions

(%)

Average

Emission

Rate

(lb NOX/ton

of clinker)a

Range of

Emission

Rates

(lb NOX/ton

of clinker)

Process Control

Modifications

<25

CemStar n/a 33 23 to 40 6.0 3.2 to 11.2

Indirect firing

with a low-NOX

burner

20 to 30 27 4 to 47 9.0 b 9.0 b

MKF

(wet kilns only)

20 to 40 c 41 28 to 59 d n/a n/a

MKF

(dry kilns only)

20 to 40 c 33 11 to 55 3.9 2.0 to 10

TDF in a

Precalcinere

35 30 to 40 2.4 2.4

SNCR 30 to 70 BSIe

50 1.2 1.2

NOX-

OUTf

40 10 to 50

n/a - not applicablea The average emission reduction and average emission rate were calculated using a simple (not weighted) average

of the available data.b There was only one source that provided emission rate data for low-NOX burners; the rest of the kilns with low-

NOX burners only provided percent reductions.c The 1994 ACT document provide one range of possible emission reductions for MKF at both wet and dry kilns.

d At the time the kiln with the 59 percent emission reduction installed MKF, it also added a Linkman control

system; the next largest percent emission reduction at a wet kiln from MKF was 35.0.

e One facility in southern California provided emission reduction data for both biosolids injection

(BSI) technology and firing tire derived fuel (TDF) in a precalciner.fThe average emissions reduction for NOXOUT® was estimated from the three tests/demonstrations described in

5.3.2.2.

Monitoring the temperature and excess air in the combustion zone as discussed in Section

5.1.1 provides optimum kiln operating conditions, which increase the energy efficiency and

78

1. European Integrated Pollution Prevention and Control Bureau (EIPPCB). Reference

Document on Best Available Techniques in the Cement and Lime Manufacturing

Industries. World Trade Center, Seville, Spain. March 2000.

productivity of the cement-making process while minimizing NOX emissions. The NOX

reduction effect of other process modifications discussed in Section 5.1 is usually difficult to

isolate from other factors. These measures can be highly site specific and data from one site

cannot be directly translated to other sites. Quite often a number of process modifications and

combustion control measures are implemented simultaneously. Process modifications can reduce

NOX emissions in cement kilns without any specific NOX control equipment. Some plants rely

on process monitoring and control and process modifications as a means to maintain NOX

emissions within their allowable limits.

The CemStar process described in Section 5.1.2.2 is being used or incorporated by 11

facilities in the United States. Several long-term and short-term tests of CemStar have found

average NOX emission reductions of 33 percent.

Combustion modifications to reduce NOX emissions include the staged combustion of air

and of fuel. Low-NOX burner systems described in Section 5.2.1.2 rely on the staged combustion

of air. Technical literature and industry publications report NOX reduction rates of 4 to 47

percent with the installation of low-NOX burners, depending on the baseline emissions, type of

kiln, type of low-NOX burner, and operating conditions.

As described in Section 5.2.2, staged combustion of fuel includes the use of preheaters/

precalciners and mid-kiln firing. Mid-kiln firing of fuels is practiced in over 20 U.S. cement

kilns and whole tires are most frequently used for the mid-kiln fuel. Data are available for

several kilns that have used or tested mid-kiln firing demonstrating NOX reductions ranging from

11 to over 59 percent.

The NOX removal controls discussed in Section 5.3 include selective catalytic reduction,

and selective noncatalytic reduction (biosolids injection and NOXOUT). SCR technology has not

been used on any cement kilns in the U.S., although pilot plant trials and feasibility studies have

been conducted in Europe. The principles of SNCR technology are applicable to preheater/

precalciner kilns. It is believed that SNCR would be difficult, if not impossible, to be used in

wet and long dry process kilns due to problems in obtaining the right temperature and retention

time. Two SNCR technologies, biosolids injection and NOXOUT®, have demonstrated NOX

emission reductions in cement kilns. Biosolids injection is being used on one kiln in Southern

California and NOXOUT has been demonstrated on two kilns in the U.S. SNCR technology is

widely practiced in Europe.

5.6 REFERENCES

79


Encyclopedia of Chemical Technology. Vol. 5. Third Edition. New York, NY. John

Wiley & Sons, Inc. 1979. pp. 163-193.

3. Yee, G.M. Suggested Control Measure for the Control of Emissions of Oxides of

Nitrogen from Cement Kilns. Presented to the State of California, Air Resources Board

for Discussion on October 21, 1981.

4. Miller, F.M. Oxides of Nitrogen. GTC Presentation, Kansas City, MO, September 20,

1977.

5. Hansen, E.R., “The Use of Carbon Monoxide and Other Gases for Process Control,” 27th

IEEE Cement Industry Technical Conference Proceedings, May 1985.

6. Mehta, P.K. Energy, Resources and the Environment - A Review of the U.S. Cement

Industry. World Cement Technology. July/August 1978.

7. Andover Technology Partners. NOx Reduction from Cement Kilns Using the CemStar

Process, Evaluation of CemStar Technology - Final Report to Texas Industries. Dallas,

Texas. April 18, 2000.

8. Battye, R., and S. Edgerton, EC/R Incorporated. “December 2, 1999 Trip Report to

Texas Industries (TXI) Riverside Cement, Oro Grande facility.” Oro Grande, CA.

Submitted to Dave Sanders, US EPA, under contract No. 68-D-98-026, work assignment

No. 2-28. August 31, 2000.

9. En-tellect Environmental Services, Inc., “Evaluation of the Effects of the CemStar

Process on a Wet Process Cement Kiln,” (no date, but includes data for July-Sept 1999).

10. Hilovsky, R.J. NOX Reductions in the Portland Cement Industry With Conversion To

Coal-Firing: Presented at the 1977 U.S. EPA Emission Inventory/Factor Workshop.

Raleigh, NC. September 13-15, 1977.

11. Radian Canada, Inc. Assessment of NOX Emission Control Technologies for Cement and

Lime Kilns. Radian Report No. 714-061-01. Prepared for Environment Canada, Contract

No. K2035-3-7044. October 1994. Pg.iv.

12. Portland Cement Association. U.S. and Canadian Portland Cement Industry Plant

Information Summary. Skokie, IL. December 31, 1998.

13. Penta Engineering Corporation Report on NOX Formation and Variability in Portland

Cement Kiln Systems Potential Control Techniques and Their Feasibility and Cost

Effectiveness. Penta Project No. 971212. Prepared for the Portland Cement Association.

PCA R&D Serial No. 2227. Skokie, IL. 1999.

80

14. Comments on Alternative Control Techniques Document - NOX Emissions from Cement

Manufacturing submitted by Greer, W.L. to William Neuffer, U.S. EPA through T.B.

Carter, APCA. October 27, 1999.

15. U.S. Environmental Protection Agency. Summary of NOX Control Technologies and

Their Availability and Extent of Application. EPA450/3-92-004. Research Triangle Park,

NC 27711. February 1992.

16. Xeller, H. Reducing NOX Formation Using a Step Burner with Exit Gas Recycling from

Preheater. World Cement. 19(3):8492. March 1988.

17. Bauer, C. PYRO-JET Burners to Reduce NOX Emissions Current Developments and

Practical Experience. World Cement. 21(4). April 1990.

18. The ROTAFLAM Kiln Burner. Product Information Brochure. Procedair Industries,

Combustion Division, Pillard Products, Louisville, KY. 1992

19. Vollan, P., and L. Klingbeil. Modernization and Capacity Increase of Kiln Line No. 6 at

the Dalen Plant, Norway. World Cement. January 1988.

20. Wolter, A. Fast Gas Trace Analysis Optimizes and Reduces the Emission of Pollutants in

Cement Plants. Zement-KalkGips No. 12, 1987.

21. Steinbiß, V.E., C. Bauer, and W. Breidenstein. Current state of development of the

PYRO-JET® burner. VDZ Kongress. 1993.

22. Thomsen, K., L.S. Jensen, and F. Schomburg. FLS-Fuller ILC-lowNOx calciner

commissioning and operation at Lone Star St. Cruz in California. ZKG International.

October 1998. pp. 542 - 550.

23. Letter and attachments from M.H. Vaccaro, Pillard Combustion Equipment and Control

Systems, to G.J. Hawkins, Portland Cement Association, re: Low NOX Rotaflam®

burner, dated January 20, 1999.

24. PSM International, “Response to USEPA Comments, 13 September 1995, on the

proposed alternative NOX RACT for a portland cement manufacturing plant located in

Thomaston, Maine and owned by Dragon Products Company,” Jan 31, 1996.

25. Renfrew, S, Process Engineer, RMC Lonestar. Calciner modification highly effective in

meeting Northern California Plant’s alkali reduction and emission control requirements.

no date.

26. Portland Cement Association and American Portland Cement Alliance. Results of the

NOX Control Presurvey Results. January 2,000.

81

27. Memorandum from Battye, R.E., and S. Edgerton, EC/R Incorporated, Chapel Hill, NC,

to B. Neuffer, U.S. EPA, RTP, NC. Summary of February 4, 2000 teleconference to

discuss results of NOX Control Presurvey Results. February 11, 2000.

28. Portland Cement Association. A New Stone Age: The Making of Portland Cement.

Skokie, IL. 1992. pg. 4.

29. Cadence Environmental Energy, Inc. www.cadencerecycling.com.

30. Battye, R., and S. Edgerton, EC/R Incorporated. “December 2, 1999 Trip Report to

Mitsubishi Cement Corporation, Cushenbury Plant.” Lucerne Valley, CA. Submitted to

Dave Sanders, US EPA, under contract No. 68-D-98-026, work assignment No. 2-28.

August 31, 2000.

31. Shumway, D.C. “Tire Derived Fuel at Mitsubishi Cement Corporation.” Received

during December 2, 1999 visit to Mitsubishi.

32. Shumway, D.C. Mitsubishi Cement Corporation’s Cushenbury Plant presented at the

IEEE West Coast Cement Industry Conference. Victorville, CA. Oct 1995.

33. Rother, R. and D. Kupper. Staged Fuel Supply - An Effective Way of Reducing NOX

Emissions. Zement-Kalk-Gips. No. 9. 1989.

34. Nielsen, P.B., and O.L. Jepsen. An Overview of the Formation of SOX and NOX In

Various Pyroprocessing Systems. Presented at the IEEE Cement Industry Technical

Conference XXXII. Tarpon Springs, FL. May 22-24, 1990.

35. Facsimile from Bennett, J., California Portland Cement Company, to Damle, A.S.,

Research Triangle Institute. August 4, 1993. Process modifications in cement kilns.

36. Benoit, M.R., E.R. Hansen, and T.J. Reese. Method for Energy Recovery from

Containerized Hazardous Waste. U.S. Patent No. 4974529. December 1990.

37. Walquist, C., Cadence Environmental Energy. “Cadence system leads to fall in NOX

emissions,” World Cement, Dec 1997, pp. 26, 27.

38. Hansen, E.R. New Way to Burn Hazardous Waste. Rock Products. April 1990.

39. Cadence Environmental Energy and Ash Grove Cement. “Mid-Kiln Fuel Entry

Benefits,” section 3 of the report, Emission, Reduction, Technology: Resource

Conservation & Recovery. (no date).

40. Letter from Edgerton, S. and T. Stobert, EC/R Inc., to Bill Neuffer, EPA, Feb 8, 2000.

Minutes from Dec 16, 1999 meeting with representatives from EPA and Cadence.

82

41. Texas Natural Resources Conservation Commission. A list of permitted NOX levels for

cement plants in the state, CEMS data as reported by the facilities for 1994 - 1999, and

information on the control technology in use at each facility.

42. May, M. and L. Walters, Jr. "Low NOX & Tire-derived Fuel for the Reduction of NOX

from the Portland Cement Manufacturing Process." Cement Americas, August 1999, pp.

10-1.

43. Letter and attachments from Bramble, Kim, Cadence, to Bill Neuffer, USEPA, re: NOX

Emission Reducing Technology, dated Feb 14, 2000.

44. Radian Corporation, "MDE Air Permit Test Report for Lehigh Portland Cement

Company, Union Bridge, Maryland Facility," January 1996.



46. Smith, J.C., and M.J. Wax. Selective Catalytic Reduction (SCR) Controls to Abate NOX

Emissions. White Paper by Wax, M. J., Institute of Clean Air Companies. September

1992.

47. Joseph, G.E., and D.S. Beachler. Student Manual, APTI Course 415 Control of Gaseous

Emissions. U.S. EPA, Air Pollution Training Institute. EPA 450/2-81-006. December

1981.

48. Campbell, L.M., D.K. Stone, and G.S. Shareef. Sourcebook: NOX Control Technology

Data. U.S. EPA, Air and Energy Engineering Research Laboratory. EPA-600/2-91-029.

July 1991.

49. Siddiqi, A.A., and J.W. Tenini. Hydrocarbon Processing. 115-124. October 1981.

50. Letter from Wax, J., Institute of Clean Air Companies, to Neuffer, W.J., U.S.

Environmental Protection Agency. August 27, 1992. Response to ACT Document -

Control of NOX Emissions from Process Heaters.

51. Haas, G.A. Selective Noncatalytic Reduction (SNCR): Experience with the Exxon

Thermal DeNOX Process. Presented at the NOX Control V Conference. Council of

Industrial Boiler Owners. Long Beach, CA. February 10-11, 1992.

52. Lin, M.L., M.J. Knenlein, Fuel Tech Inc. “Cement Kiln NOX Reduction Experience

Using the NOXOUT® Process,” proceedings of the 2000 International Joint Power

Generation Conference, Miami Beach, FL, July 23-26, 2000.

83

53. Kokkinos, A., J.E. Cichanowicz, R.E. Hall, and C.B. Sedman. Stationary Combustion

NOX Control: A Summary of the 1991 Symposium. J. Air Waste Manage. Assoc. 1252.

1991.

54. Teixeira, D. Widening the Urea Temperature Window. In Proceedings of 1991 Joint

Symposium on Stationary Combustion NOX Control. NTIS. 1991.

55. Kupper, D., and Brentrup, L. SNCR Technology for NOX Reduction in the Cement

Industry. World Cement 23(3):4-9. March 1992.

56. Scheuer, A., Non-catalytic reduction of NO with NH3 in the cement burning process.

Zement-Kalk-Gips, No. 3/1990, Wiesbaden, Germany.

57. Sun, William H., Nalco Fuel Tech. NOXOUT® Process Demonstration on a Cement

Kiln/Calciner, Ash Grove Cement, Seattle Plant, Seattle, Washington. October 28, 1993.

58. Sun, et. al. Reduction of NOX Emissions from Cement Kiln/ Calciner through the Use of

the NOXOUT® Process. Presented at the International Specialty Conference on Waste

Combustion in Boilers and Industrial Furnaces. Kansas City, MO. April 1994.

59. Interoffice Correspondence from McAnany, L. to H. Knopfel, H, LaFarge Corporation.

October 26, 1998. re: Fuel Tech NOXOUT® Testing.

60. PSM International Inc. and Penta Engineering Corp. Review of Nalco Fuel Tech

NOXOUT® Program for Mid-Kiln Injection Urea to Reduce NOX at the Colton California

Plant of California Portland Cement Company. October 26, 1994.

61. Biggs, H.O., Plant Manager, Mitsubishi Cement Corporation. Biosolids Injection

Technology: An Innovation in Cement Kiln NOx Control. (no date). Received during

December 1999 trip report.

62. Shumway, D.C. Tire Derived Fuel at Mitsubishi Cement Corporation. (no date)

Received during December 1999 site report.

63. McInnes, R., and M.B. von Wormer. Cleaning Up NOX Emissions. Chem. Eng. 130-135.

September 1990.



NC. March 1994.


U.S. EPA, RTP, NC. Derivation and Data Supporting Development of Cement Plant

NOX Emission Rates. September 15, 2000.

84

6.0 COSTS OF NOX CONTROL TECHNIQUES

This chapter presents the cost estimates for the NOX emission control techniques

discussed in Chapter 5. Section 6.1 presents the cost methodology used to develop capital and

annual operating costs for these techniques. Based upon the distribution of the type of kilns used

in the cement industry and their typical capacities, model plants were developed to perform cost

calculations. Section 6.2 presents costs of selected incombustion and postcombustion control

approaches. The cost effectiveness of different control approaches is discussed in Section 6.3.

All costs presented in this chapter are in 1997 dollars.

6.1 COST CALCULATION METHODOLOGY

The cost calculation methodology is dependent upon the definition of model plants and

the guidance provided by EPA in the OAQPS Control Cost Manual.1 The definition of the model

plants, calculation of capital costs and annual operating costs is presented in this section.

6.1.1 Model Plants

As discussed in Chapter 3, existing cement kilns in the United States may be grouped in

four types: wet, long dry, preheater, and precalciner types. Coal is the most common fuel used in

all types of kilns.2 Several types of waste-derived fuels are being used in the portland cement

industry to replace coal and reduce NOX emissions. As seen from data presented in Chapter 4,

the NOX emissions from individual kilns expressed as lb NOX/ton of clinker do not seem to

depend on the kiln capacity. Therefore, only two capacities of the kilns of a given type are used

to define model plants for each of the kiln types. Each of the four kiln types has typical energy

consumption and NOX emission rates as shown in Table 6-1 describing model plant parameters.

The model plant kilns were assumed to be in continuous-duty operation and were assumed to

operate 8,000 hours per year which allows scheduled downtime for maintenance operations.3

Although waste-derived fuels are finding increasing applications in cement kilns, coal provided

more than 82 percent of the energy requirement of the cement industry.2 Model plants were

assumed to use 100 percent coal as a fuel and where available, a percentage of coal and waste-

derived fuels (i.e., for mid-kiln firing 85% coal and 15% tire-derived fuel were used).

6.1.2 Capital Cost Estimation

The total capital investment is the sum of the direct cost (which is the purchased

equipment costs and direct installation costs), indirect installation costs, contingency costs, sales

taxes, freight, and production downtime. The purchased equipment costs (PECs) used in this

chapter for each control technology are based on cost information provided by vendors or from

data provided by existing facilities. Table 6-2 provides a list of various cost elements included in

the capital costs. Where installation costs were not provided by vendors, direct and indirect

installation costs were developed using the factors 45 and 33 percent, respectively, of PEC, per

guidelines in the EPA OAQPS Control Cost Manual.1 A contingency factor of 20 percent was

85

TABLE 6-1. CEMENT KILN MODEL PLANTS FOR COST CALCULATIONS

Model

no. Kiln type

Capacity

(tons

clinker/hr)

Heat input

rate (MM

Btu/ton

clinker)

Uncontrolled NOX

emissions

Gas flow

rate at stack

location

(dry std

ft3/min)

(lb/ton

clinker) (lb/hr)

1 Wet 30 6.0 9.7 291 59,100

2 Wet 50 6.0 9.7 485 98,500

3 Long dry 25 4.5 8.6 215 38,500

4 Long dry 40 4.5 8.6 344 61,500

5 Preheater 40 3.8 5.9 236 53,200

6 Preheater 70 3.8 5.9 413 93,000

7 Precalciner 100 3.3 3.4 340 118,500

8 Precalciner 150 3.3 3.4 510 176,000

Average stack gas temperature ~150C (300F).

Average stack gas moisture content ~12%.

Average particulate loading in stack gas ~0.01 grains/dry std ft3.

added to the vendor costs in all cases to cover contingencies as listed in Table 6-2.1 The capital

costs of in-combustion approaches such as low NOX burners and postcombustion approaches

such as selective noncatalytic reduction are related to the clinker production capacity of the kiln

as well as the energy requirement of the kiln per unit amount of clinker production.

6.1.3 Annual Operating Costs

Annual operating costs are composed of the direct operating costs of materials and labor

for maintenance, operation, utilities, material replacement and disposal and the indirect operating

charges, including plant overhead, general administration, and capital recovery charges.

Table 6-3 lists the typical values used for these costs. A brief description is provided below for

each component of the direct annual operating costs used in the cost evaluation.

6.1.3.1 Utilities. The utility requirements for the control techniques consist of electricity

and/or compressed air to power control instrumentation and auxiliary equipment and the energy

requirements for vaporization and injection of ammonia for SCR systems. The cost for

electricity and compressed air is considered to be negligible relative to the other operating costs.

The credit applied (tipping fee) for burning tires is an average value.4 Tire tipping fees

are highly variable showing a large regional variation and large fluctuations in the market. The

average tipping fee used in this analysis is within the 1997 range of $20 to $200 credit/ton of

86

tires provided by Waste News.5 A direct access of the Waste News - Current Commodity Pricing

demonstrated a range in tipping fee credits of $140 to $75 in New York; $125 to $65 in Miami,

Florida; $100 to $75 in Atlanta, Georgia; $150 to $75 in Houston, Texas; $85 to $75 in Chicago,

Illinois; $85 to $20 in Denver, Colorado; $100 to $42 in Los Angeles; California: and $200 to

$100 in Seattle, Washington.6

TABLE 6-2. CAPITAL INVESTMENT COMPONENTS FOR

EMISSION CONTROL DEVICE COST EVALUATION 1

Capital Investment Cost Elements

Direct costs (DC)

Purchased equipment costs (PEC):

Control device and auxiliary equipment

Instrumentation

Direct installation costs (DIC) - 45 percent of PEC:

Foundations and supports

Handling and erection

Electrical

Piping

Insulation for ductwork

Painting

Indirect installation costs (IIC) - 33 percent of PEC:

Engineering

Construction and field expenses

Contractor fees

Startup

Performance test

Model study

Contingencies (C) - 20 percent of PEC:

Equipment redesign and modifications

Cost escalations

Delays in startup

Sales taxes (3 percent of PEC)

Freight (5 percent of PEC)

Production downtime (two days loss of production times average market value per ton of

clinker)*

* Average market value per short ton of clinker is $72.59.7

87

TABLE 6-3. ANNUALIZED COST ELEMENTS AND FACTORS 1

Direct annual costs (DC)

1. Utilities:

Coal8 $32.41 per short ton

Electricity9 $0.05 per kwh

Natural gas10 $3.59 per 1000 ft3

Tires11 -$42.50 per ton

2. Operating labor

Operator labor12 $22.12 per hour

Supervising labor1 15 percent of operator labor

3. Maintenancea

Maintenance labor $24.33 per hour times 0.5 hours per 8 hour

shiftb

Maintenance materials 100% of maintenance labor

Indirect annual costs (IC)a

Overhead 60% of operating labor, supervisory labor,

maintenance labor and materials

Property tax 1% of total capital cost

Insurance 1% of total capital cost

Administrative charges 2% of total capital cost

Capital recovery capital recovery factor times total capital

investment

TOTAL ANNUAL COST DC + ICaReferences for costs are included in Section 6.1.3.bMaintenance labor is 1.1 times the operator labor.1

6.1.3.2 Operating and Supervising Labor. No postcombustion NOX control

technologies were identified as currently operating on a cement kiln in the United States.

Therefore, information for typical operating labor requirements from the cement industry was

unavailable. A requirement of 0.5 hour of operator attention was assigned for an 8-hour shift, for

88

all technologies considered, regardless of the plant size. Operator wage rates were estimated to

be $22.12/hr in 1997.12 Supervisory labor costs were estimated to be 15 percent of the operating

labor costs consistent with the OAQPS Control Cost Manual.1

6.1.3.3 Maintenance. Specific maintenance costs were not available from the control

system vendors and manufacturers. The guidelines for maintenance costs in the OAQPS Control

Cost Manual suggest a maintenance labor cost of 0.5 hours per 8-hour shift and a maintenance

material cost equal to this labor cost.1

6.1.3.4 Overhead. An annual overhead charge of 60% of the total maintenance cost was

used, consistent with guidelines in the OAQPS Control Cost Manual.1 As described above, the

maintenance cost is 0.5 hours per 8-hour shift and a maintenance material cost equal to this labor

cost.

6.1.3.5 Property Taxes. The property taxes were calculated as 1 percent of the total

capital cost of the control system, as suggested in the OAQPS Control Cost Manual.1

6.1.3.6 Insurance. The cost of insurance was calculated as 1 percent of the total capital

cost of the control system, as suggested in the OAQPS Control Cost Manual.1

6.1.3.7 Administrative Charges. The administrative charges were calculated as 2

percent of the total capital cost of the control system, consistent with the OAQPS Control Cost

Manual.1

6.1.3.8 Capital Recovery. In this cost analysis the capital recovery factor (CRF) is

defined as1:

CRF = i (1 + i)n / ( (1 + i)n - 1) = 0.1098

where

i is the annual interest rate = 7 percent, and

n is the equipment life = 15 years.

The CRF is used as a multiplier for the total capital cost to calculate equal annual payments over

the equipment life.

6.2 COSTS OF NOX CONTROL APPROACHES

As discussed in Chapter 5, feasible NOX control approaches include process

modifications, combustion modifications, and NOX removal controls. Process modifications

include combustion zone control of temperature and excess air, feed mix composition, kiln fuel,

and increasing thermal efficiency of the kiln. Combustion modifications include staged

89

combustion of air and staged combustion of fuel. NOX removal controls that are presented

include selective catalytic and noncatalytic reduction of NOX using either ammonia or urea. This

chapter includes costs for approaches and technologies that will reduce NOX emissions and

focuses on four technologies; changing the feed mix composition (CemStar), installation of a low

NOX burner (staged combustion of air), installation of a mid-kiln firing system (staged

combustion of fuel), and noncatalytic reduction of NOX using biosolids (biosolids injection).

6.2.1 Process Modifications

As discussed in Section 5.1, process modifications can be highly site specific and data

from one site cannot be directly translated to other sites. Data are not available to determine

costs of individual process modifications. Quite often a number of process modifications and

combustion control measures are implemented simultaneously. Similar to combustion process

control approaches, process modifications have also shown to reduce energy requirement and

increase productivity, thus providing an economic incentive to implement them in addition to

NOX reduction.

6.2.1.1 Combustion Zone Control of Temperature and Excess Air. Approaches

aimed at improving the energy efficiency of the process indirectly reduce NOX emissions per ton

of clinker product. These approaches rely on continuous monitoring of O2 and CO and in some

cases NOX emissions for controlling the excess air, fuel rate, and the combustion zone

temperature. These measures are usually undertaken to increase process energy efficiency by

reducing over-burning of the clinker. Maintaining the combustion zone temperature to a

necessary minimum value using process control systems minimizes both the process energy

requirement and increases refractory life. Because continuous monitoring of emissions is

necessary for efficient process control, the cost of monitors is not considered as a NOX control

cost. Further, the information obtained during this study indicated that some plants relied on

process monitoring, including NOX monitoring, as a means to maintain NOX emissions within

their respective permit limits.

Based on existing installations, the cost of a commercially available kiln process control

system is in the neighborhood of $750,000.13 The resulting savings due to reduced energy and

fuel requirements and increased refractory life were estimated to be about $1.37 per short ton of

clinker. Thus, for a cement kiln facility producing 300,000 tons/year of clinker the reduced cost

of producing cement is expected to recover process control installation costs in less than 2 years.

90

6.2.1.2 CemStar Process. As discussed in section 5.1.2.2, the CemStar process (which

involves the substitution of steel slag for raw materials) reduces the kiln temperature in the

region of the flame and results in lower NOX emissions. In addition, because the chemical

composition and structure of steel slag is similar to cement, the heat required to convert a ton of

steel slag to clinker is substantially lower than the heat required to convert a ton of raw materials

to clinker.14 The costs associated with installing this process are primarily material handling

equipment for the steel slag. Cost information was obtained from TXI and are summarized in

Table 6-4.15 The cost of the material handling equipment can range from $200,000 to $500,000.

TABLE 6-4. BASIS FOR COST ANALYSIS OF CEMSTAR (1997 $)

Capital Cost of Material

Handling Equipment

$500,000

Type of Kiln Wet

Primary Fuels Coal and natural gas

Kiln Production Rate

Before CemStar 42 tons/hour

After CemStar 45 tons/hour

Quantity of Steel Slag 3.2 tons/hour

Average kiln heat requirement 5.00 MMBtu/ton

Total Capital Investment $1,176,000

Annualized Costa $220,000a Includes cost of steel slag, royalties, and credit for the reduction in raw materials.

CemStar model plants costs could not be developed because the addition of steel slag is

completely plant dependant. There is no set ratio of steel slag injection to kiln production rate.

The amount of steel slag needed depends on the plants raw materials. The ratio can vary

anywhere from five to ten percent addition of steel slag, based on kiln production. For the

example presented in this document, the addition of steel slag was 7.7 percent of the kiln

production prior to production with the CemStar process. The addition of steel slag typically

reduces the need for iron used in raw material feed. Monetary savings from the reduction in iron

can range from $0.5 to $1.00 per ton of clinker produced. A reduction in shale and/or clay may

also result from the addition of steel slag. The amount of shale and/or clay reduction varies

based on each facilities raw materials. Depending on the raw material characteristics, the need

for shale and/or clay may be eliminated. CemStar charges royalties that are paid by the facility

installing the technology. The royalties are approximately $16 per ton of steel slag used.16

91

Cost savings associated with the CemStar process are based on production increase with

the addition of steel slag compared to the cost benefit. Due to steel slag addition you get

approximately one ton of clinker per ton of steel slag added. Steel slag cost $5-15 per ton,15

whereas clinker cost $72.59 per ton. Average cost savings equals $62.59 per ton times increase

in production. Most plants increase production by five to ten percent with the addition of the

CemStar process.

6.2.2 Combustion Modifications

As discussed in section 5.2 there are several combustion modifications that can be

implemented to reduce NOX emissions. This section presents costs for low NOX burners (staged

combustion of air) and mid-kiln firing (staged combustion of fuel).

6.2.2.1 Low NOX Burners. Cement kiln burners, specifically marketed as low NOX

burners, require an indirect-fired kiln system. Therefore, to install a low NOX burner in an

existing direct-fired kiln, it is necessary to convert the kiln-firing system to an indirect firing

system. Two sets of costs are therefore developed: (1) to install a low NOX burner in an existing

indirect-fired kiln, and (2) to install a low NOX burner in an existing direct-fired kiln. In the first

case, only the costs of the low NOX burner equipment are considered, whereas in the second case

the costs of conversion of a direct-fired system to an indirect-fired system are added to the low

NOX burner cost.

Information was obtained from a supplier of low-NOX burners regarding costs and heat

duty.17 The cost of a burner depends upon the size or heat duty as well as on the number of

different types of fuels that can be burned, e.g., only coal, or coal and gas, or coal, waste-derived

liquid fuel and gas. The cost also depends on whether the burner is being installed in a new plant

or is a retrofit in an older plant. The PEC of a low NOX burner retrofit using coal as a fuel is

typically about $100,000 for a 200 MM Btu/hr heat duty. For a multi-channel burner the cost is

higher. The capital cost of a multi-channel retrofit low NOX burner is about 100 percent greater

than that for a single channel burner for the same heat duty.

From the limited available data a linear correlation (R2 = 0.98) developed for an

approximate purchase cost for a retrofit application as a function of heat duty is given as:

PEC = 172,000 + 152 H

where

PEC = Multi-channel low NOX burner purchase equipment cost in $, and

H = Burner heat duty in MM Btu/hr.

The cost of a single channel low NOX burner is obtained by dividing the PEC of a multi-channel

burner by 2.

92

For each model plant described in Table 6-1 purchase equipment costs for multi-channel

burners were determined based on the heat duty needed by the kiln. For wet, long dry, and

preheater kilns all the required heat is assumed to be provided by the low NOX burner, whereas

for precalciner kilns only 60 percent of the heat duty is assumed to be provided by the low NOX

burner at the hot end of the kiln. The capital costs for retrofiting the eight model plants described

in Table 6-1 in an existing indirect-fired kiln are given in Table 6-5. Direct installation, indirect

installation, and contingency costs were assumed to be 45, 33, and 20 percent, respectively, as

discussed in Section 6.1.2. The capital costs of retrofit low NOX burners for the eight model

plants ranged from $473,000 for the small long dry kiln to $966,000 for the large

preheater/precalciner kiln. The capital costs for retrofitting on a wet kiln compare well with the

$500,000 total installed cost estimated by a cement company.18

The annualized costs for low NOX burners in an existing indirect-fired kiln are presented

in Table 6-6. No additional costs for utilities were deemed necessary for NOX control purposes.

As described in section 6.1.3, 0.5 hours of operating labor were added per 8-hour shift and

maintenance costs were estimated as 0.5 hours of labor per 8-hour shift with maintenance

material costs equal to this labor cost. Indirect annual costs were determined as described in

Section 6.1.3. The total annualized costs for the eight low NOX burner retrofits ranged from a

low of $130,000/year for the small long dry kiln to a high of $204,000/year for the large

preheater/precalciner kiln.

Conversion of a direct-fired kiln to an indirect-fired kiln reduces the amount of primary

air and increases the proportion of secondary air input to the kiln. The total cost to convert an

existing dry process facility with two kilns, with a combined 100 tons/hr clinker capacity and a

225 MM Btu/hr heat duty, was $5.6 million in 1998.19,20 The equipment list included a Pfister

coal metering system, coal mill dust collector, Pillard burner and trolley, coal fire detection

system, carbon dioxide inerting system, coal conveying blowers, pulverized coal bins, pulverized

coal bin dust collector, instrumentation, primary air fan, and ductwork. Using the data provided

by the facility and the cost calculation methodology presented in section 6.1 (which adds 8

percent PEC cost for sales tax and freight, 45 percent PEC cost for direct installation, 33 percent

PEC cost for indirect installation, and 20 percent PEC cost for contingencies) the total installed

capital cost is estimated at $3.8 million (in 1997 dollars). The actual cost of $5.6 million (in

1998 dollars) for the same facility includes $2.3 million for contractor engineering and project

management. When the costs are adjusted to include engineering and project management as

part of the indirect installation costs1 (approximately $550,000), there is agreement between the

two estimates.

Since the $3.8 million equipment cost estimate was for two parallel systems, the cost of

one conversion system to process coal for a 50 ton/hr dry facility21 was considered to be $1.88

million in 1997 dollars. The amount of coal processed is proportional to heat requirement. For a

dry process, the energy requirement is approximately 4.5 MM Btu/ton. Therefore, the cost of

93

TABLE 6-5. CAPITAL COSTS FOR RETROFIT LOW-NOX BURNERS IN AN EXISTING INDIRECT-FIRED KILN (1997 $)

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat duty

(MM

Btu/hr) PEC ($)

Freight

and sales

tax ($)

Installation costs $

Contingency

costs ($)

Production

Downtime

($)

Total

capital

costs ($)Direct Indirect

1 Wet 30 180 198,000 16,000 89,000 65,000 40,000 105,000 511,000

2 Wet 50 300 216,000 17,000 97,000 71,000 43,000 174,000 618,000

3 Long dry 25 113 187,000 15,000 84,000 61,000 37,000 87,000 473,000

4 Long dry 40 180 198,000 16,000 89,000 65,000 38,000 139,000 546,000

5 Preheater 40 152 193,000 15,000 87,000 64,000 39,000 139,000 538,000

6 Preheater 70 266 210,000 17,000 95,000 69,000 42,000 244,000 678,000

7 Precalciner 100 330 200,000 16,000 90,000 66,000 40,000 348,000 761,000

8 Precalciner 150 495 215,000 17,000 97,000 71,000 43,000 523,000 966,000

94

TABLE 6-6. ANNUALIZED COSTS FOR RETROFIT LOW-NOX BURNERS IN AN EXISTING INDIRECT-FIRED KILN(1997 $)

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat duty

(MM

Btu/hr)

Maintenance

costs ($/yr)

Other

labor ($)

Overhead

costs ($/yr)

Taxes

insurance

admin.

($/yr)

Capital

recovery

($/yr)

Total

annualized

costs ($/yr)

1 Wet 30 180 24,400 12,700 22,200 20,500 56,200 136,000

2 Wet 50 300 24,400 12,700 22,200 24,700 67,900 152,000

3 Long dry 25 113 24,400 12,700 22,200 18,900 51,900 130,000

4 Long dry 40 180 24,400 12,700 22,200 21,900 60,000 141,000

5 Preheater 40 152 24,400 12,700 22,200 21,500 59,000 140,000

6 Preheater 70 266 24,400 12,700 22,200 27,100 74,400 161,000

7 Precalciner 100 330 24,400 12,700 22,200 30,400 85,600 173,000

8 Precalciner 150 495 24,400 12,700 22,200 48,600 106,000 204,000

95

PEC for model plant Heat requirement for model plant

835 000 225

0 6

,

.

=

firing system conversion to process coal to provide 225 MM Btu/hr equivalent energy is

considered to be $835,000. Cost of firing system conversion for other heat capacities was

estimated using 0.6 power rule:

This cost includes the PEC for installing a low NOX burner. For each model plant

described in Table 6-1 the PEC for the firing system conversion as well as for the multi-channel

burner was determined based on the heat duty needed by the kiln. For wet, long dry, and

preheater kilns all the required heat is assumed to be provided by the low NOX burner, whereas

for precalciner kilns only 60 percent of the heat duty is assumed to be provided by the low NOX

burner at the hot end of the kiln. The capital costs for retrofitting the eight model plants in an

existing direct-fired kiln are given in Table 6-7. The capital costs ranged from $1.21 million for

the small long dry kiln to $2.54 million for the large precalciner kiln.

The annualized costs for low NOX burners in an existing direct-fired kiln are presented in

Table 6-8. Operating labor was assumed to be 0.5 hour per 8-hour shift. Maintenance labor

costs were assumed to be 0.5 hour per 8-hour shift and maintenance materials were assumed to

be equal to 100% of the maintenance labor cost. The total annualized costs for the eight low

NOX burner retrofits in existing direct-fired kilns ranged from $241,000 for the small dry kiln to

$439,000 for the large precalciner kiln. These values agree well with the costs, of converting a

direct fired kiln to an indirect fired kiln and installing a low-NOX burner, presented in the 1994

ACT.18,22,23

6.2.2.2 Mid-Kiln Firing As discussed in Section 5.2.2.2, secondary combustion of fuel

reduces thermal NOX formation in cement kilns. Modification of a long kiln for secondary

combustion of fuel is termed mid-kiln firing. The amount of fuel NOX generated during the

secondary combustion determines the net effectiveness of this technique for NOX control. The

costs associated with this process are those for kiln modifications necessary to facilitate

secondary combustion of fuels as well as those for a conveying system required for the secondary

fuel. Mid-kiln firing is now a proven technology with twenty one cement kilns in the U.S. that

utilize mid-kiln firing. Costs were obtained from a vendor for four scenarios representing two

wet kilns and two dry kilns.4 Typically, the secondary combustion approach allows burning

waste-derived fuels and, as such, reduces the overall cost for the fuel. The purchased equipment

cost for each of the four kilns is approximately $1.5 million. This cost includes approximately

$1.0 million for a completely automated system for injecting tires or containerized solid or liquid

fuels and $500,000 for the modifications to the kiln. The cost of a fuel conveying system can be

considerably lower for a semiautomatic, labor intensive system and may be expected to depend to

a small extent upon the fuel conveying capacity needed. Costs for mid-kiln firing are not

applicable to preheater or precalciner type kilns.

96

TABLE 6-7. CAPITAL COSTS FOR RETROFIT LOW-NOX BURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat duty

(MM

Btu/hr) PEC ($)

Freight

and sales

tax ($)


Contingency

costs ($)

Production

Downtime

($)

Total

capital


1 Wet 30 180 724,000 58,000 326,000 239,000 145,000 105,000 1,600,000

2 Wet 50 300 984,000 78,700 443,000 325,000 197,000 174,000 2,200,000

3 Long dry 25 113 546,000 43,700 246,000 180,000 109,000 87,100 1,210,000

4 Long dry 40 180 724,000 60,000 326,000 239,000 145,000 139,000 1,630,000

5 Preheater 40 152 655,000 52,400 295,000 216,000 131,000 139,000 1,490,000

6 Preheater 70 266 916,000 73,200 412,000 302,000 183,000 244,000 2,130,000

7 Precalciner 100 330 767,000 61,400 345,000 253,000 153,000 348,000 1,930,000

8 Precalciner 150 495 978,000 78,300 440,000 323,000 196,000 523,000 2,540,000

97

TABLE 6-8. ANNUALIZED COSTS FOR RETROFIT LOW-NOX BURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat duty

(MM

Btu/hr)

Maintenance

costs ($/yr)

Operating

labor ($)

Overhead

costs ($/yr)

Taxes

insurance

admin.

($/yr)

Capital

recovery

($/yr)

Total

annualized

costs ($/yr)

1 Wet 30 180 24,300 12,700 22,200 63,900 175,000 298,000

2 Wet 50 300 24,300 12,700 22,200 88,100 242,000 389,000

3 Long dry 25 113 24,300 12,700 22,200 48,500 133,000 241,000

4 Long dry 40 180 24,300 12,700 22,200 65,300 179,000 304,000

5 Preheater 40 152 24,300 12,700 22,200 59,500 163,000 282,000

6 Preheater 70 266 24,300 12,700 22,200 85,200 234,000 378,000

7 Precalciner 100 330 24,300 12,700 22,200 77,100 212,000 348,000

8 Precalciner 150 495 24,300 12,700 22,200 102,000 279,000 439,000

98

Approximate capital investment costs were developed by assuming a total of $1.5 million

purchased equipment cost for kiln modifications and the fuel conveying and metering system for

the four model plants. In this example approximately 15% of the heat duty is from tire derived

fuel. This assumption results in a fuel credit (for the coal) as well as a tipping fee for the tires

(also a credit). Because the purchased equipment cost does not vary with the heat duty of the

kiln, the 0.6 power rule does not apply. Total capital investment was calculated using the

methodology presented in section 6.1. It should be noted that the costs estimated are higher than

the actual installation costs reported by the vendor.

The total capital costs for mid-kiln firing conversion of the four wet and long dry model

kilns are given in Table 6-9. The total capital investment costs range from $3.15 million for a

small long dry kiln to $3.24 million for a large wet kiln. The annualized costs for the mid-kiln

firing conversions are presented in Table 6-10. Operating labor was assumed to be 0.5 hour per

8-hour shift. Maintenance labor costs were assumed to be 0.5 hour per 8-hour shift and

maintenance materials were assumed to be equal to 100% of the maintenance labor cost. The

annualized costs ranged from a credit of $370,000 for the large wet kiln to a high cost of

$189,000 for the small long dry kiln.

These annualized costs were developed with a fuel credit (for the fuel that was replaced

with waste tires) as well as a tire tipping fee. In 1998 270 million scrap tires were generated and

the estimates of tires in stockpiles range from 500 million to 3 billion.24 Although the tipping

fees for tires may decline as markets for used tires increases, tire tipping fees are not likely to

disappear in the near future. In 1997, average national tipping fees for tires ranged from $20 to

$200 per ton (for whole tires).5 The annualized cost of mid-kiln firing without a tire tipping fee

(but including the fuel credit: assuming the tires or other waste derived fuels are free) ranges

from $140,000 for the large wet kiln to a high cost of $380,000 for the small long dry kiln.

6.2.3 NOX Removal Controls

Two NOX removal controls that are demonstrated in the United States for cement kilns

are biosolids injection and NOXOUT®. As discussed in Section 5.3.2, both of these technologies

are only applicable to preheater/precalciner kilns. The capital costs of this control technique

primarily include the cost of an injection system for either ammonia- or urea-based reagent,

delivery system plus storage tanks, and control instrumentation. Operating costs include the cost

of reagents and additives used, additional electricity cost for reagent pumping, and fuel penalty

cost along with operating labor and maintenance requirements.

6.2.3.1 Biosolids Injection Process. As discussed in section 5.3.2.1, the biosolids

injection process (which involves the injection of biosolids into a precalciner kiln) reduces the

NOX that was formed in the kiln. Biosolids injection has been installed on one kiln in Southern

California and the costs of the installation were obtained for that facility.3,25 The costs associated

with installing this technology include the sludge system and the sludge conveying system and

99

TABLE 6-9. CAPITAL COSTS FOR MID-KILN FIRING CONVERSION (1997 $)

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat duty

(MM

Btu/hr) PEC ($)

Freight

and sales

tax ($)


Contingency

costs ($)

Production

Downtime

($)

Total

capital


1 Wet 30 180 1,490,000 119,000 670,000 491,000 298,000 105,000 3,170,000

2 Wet 50 300 1,490,000 119,000 670,000 491,000 298,000 174,000 3,240,000

3 Long dry 25 113 1,490,000 119,000 670,000 491,000 298,000 87,100 3,150,000

4 Long dry 40 180 1,490,000 119,000 670,000 491,000 298,000 139,000 3,210,000

TABLE 6-10. ANNUALIZED COSTS FOR MID-KILN FIRING CONVERSION (1997 $)

Model

no.

Kiln

type

Kiln

capacity

(tons

clinker/hr)

Heat duty

(MM

Btu/hr)

Maintenance,

other labor,

and overhead

costs ($/yr)

Taxes,

insurance,

admin.

($/yr)

Capital

recover

y ($/yr)

Disposal

revenue

($/yr)

Fuel Credit

($/yr)

Licence

Fee ($/yr)

Total

annualized

costs ($/yr)

1 Wet 30 180 59,200 127,000 348,000 (306,000) (300,000) 54,000 (14,600)

2 Wet 50 300 59,200 130,000 356,000 (510,000) (500,000) 90,000 (370,000)

3 Long dry 25 113 59,200 126,000 346,000 (190,000) (185,000) 34,000 189,000

4 Long dry 40 180 59,200 128,000 352,000 (306,000) (300,000) 54,000 (9,340)

100

are summarized in Table 6-11 use of this technology results in a cost savings associated with the

tipping fees for the biosolids. The annual costs include operating labor (assumed to be 0.5 hour

per 8-hour shift), maintenance labor costs (assumed to be 0.5 hour per 8-hour shift), maintenance

materials (assumed to be equal to 100% of the maintenance labor cost), credit for the biosolids

tipping fee, and an electricity penalty of an additional 3% increase in fan capacity. Biosolid

tipping fees range from $0.00 to $10.00 per wet ton. An average value of $5.00/ton was used in

this analysis.

TABLE 6-11. BASIS FOR COST ANALYSIS OF BIOSOLIDS INJECTION (1997 $)

Purchased Equipment Cost $240,000

Type of Kiln Preheater/precalciner

Primary Fuels Coal and tire derived fuel

Kiln Production Rate 215 tons/hour

Quantity of Biosolids 20 tons/hour

Average kiln heat

requirement

680 MMBtu/hour

Total Capital Investment $1,200,000

Annualized Cost ($322,000)a

a Based on a biosolids tipping fee of $5.00/ton.

6.2.3.2 NOXOUT®. As discussed in section 5.3.2.2, the NOXOUT® process using either

ammonia or urea to reduce NOX emissions from cement kilns has been used successfully in

Europe. Two demonstrations of this technology26,27 for application to cement kilns has been

made in the United States but there are no cement kilns currently operating in the United States

using this technology. Costs for this technology were obtained from the equipment vendor for

two preheater/precalciner kilns and are summarized in Table 6-12.28,29 The costs presented in

Table 6-12 are consistent with values previously obtained and presented in the Alternatives

Control Techniques Document – NOX Emissions from Cement Manufacturing.30,31,32,33

In addition to the vendor costs and the published literature, cost analyses were available

from two facilities.27,34 The presented costs for both of these installations were much higher than

the costs presented by the Vendor. It should be noted that the second facility has a long dry kiln

and NOXOUT® is generally not recommended for a mid-kiln installation due to the difficulties in

providing for continuous injection of the reagent.

101

TABLE 6-12. BASIS FOR COST ANALYSIS OF NOXOUT® (1997 $)

Capital Cost of Material

Handling Equipment

Kiln A Kiln B

Type of Kiln Preheater/precalciner Preheater/precalciner

Kiln Production Rate 92 tons clinker/hour 133 tons clinker/hour

Average kiln heat

requirement

320 MMBtu/hour 440 MMBtu/hour

Total Capital Investment $1,060,000 $1,200,000

Annualized Cost $560,000a $2,000,000a

a Includes cost of reagent.

6.2.3.3 Selective Catalytic Reduction. Although no selective catalytic reduction (SCR)

systems are currently being used on cement plants in the United States, this control technique has

been applied successfully in other industries and pilot plant trials have been conducted in Europe.

Capital costs for this control approach would include cost of the SCR unit, ammonia storage

tank, and an ammonia heating/ vaporization injection system along with equipment needed for

preheating flue gases to an appropriate temperature. Operating costs would include the cost of

ammonia reagent, dilution steam, catalyst replacement and disposal costs, and energy cost

associated with reheating the kiln exhaust gases as well as the operating labor and maintenance

costs.

Since the SCR technology has not been proven in cement plants in the United States,

approximate capital and operating costs as applicable to the model plants were not available from

any of the SCR control system vendors in the United States. The following information was first

presented in the 1994 ACT document and is repeated here. An equipment cost estimate of an

SCR system was submitted by a Japanese supplier to a cement company in the United States in

1991.35 For a dry long kiln with 1,120 tons/day (47 tons/hr) clinker capacity, the estimated

equipment cost was 1 billion/Yen. With a 1992 exchange rate of 108 Yen/$ and assuming 5

percent inflation, the estimated cost in 1992 U.S. dollars was about 9.72 million. This equipment

cost estimate included SCR catalyst, SCR reactor, gas/gas heat exchanger, heater, ammonia

injection grid, ammonia storage tank, ammonia vaporizer and supply unit, induced draft fan,

instrumentation and all piping and ductwork. The reactor temperature was assumed to be 350 C

(660 F) and design NOX removal efficiency was 80 percent. Since the reactor, heat exchanger,

and gas heater design strongly depend upon the flow rate of flue gas to be treated, the equipment

costs for the model plants may be scaled based upon flue gas flow rate:

PEC for model 1

PEC for model 2

Gas flow for model 1

Gas flow for model 2=

0 6.

102

Table 6-13 presents estimated capital costs for the eight model plants. Direct and indirect

installation costs were assumed to be 45 and 33 percent of PEC, respectively, and an additional

20 percent contingency cost was added to determine total capital cost for the SCR systems. The

estimated capital costs range from $9.9 million for the small dry long kiln to $24.6 million for

the large precalciner kiln.

The estimated annualized costs for SCR systems on the eight model plants are shown in

Table 6-14. These include operating labor and maintenance costs, capital recovery, gas

reheating, ammonia reagent, and catalyst replacement costs.35,36 The individual operating costs

were obtained by appropriately scaling the vendor provided operating costs to the model plants.

The total annualized costs ranged from $2.5 million/yr for the small long dry kiln to $7.2 million

for the large precalciner kiln.

6.3 COST EFFECTIVENESS OF NOX CONTROLS

Cost effectiveness for the model plants was determined for three technologies for which

detailed costs could be developed as presented in the last section: low NOX burners (on an

existing indirect fired system and with conversion to an indirect firing system), and mid-kiln

firing (with a credit for firing tires or just firing coal). Limited cost data are available for a

CemStar, biosolids injection, or NOXOUT® installation in the U.S. Cost effectiveness was

calculated by dividing the total annualized cost of a given technology by the annual NOX

reduction likely to be achieved by that technology and is expressed in the units of $/ton of NOX

removed. Cost effectiveness was determined for each of the model plant scenarios.

6.3.1 CemStar

As discussed in section 6.2.1.2, the costs of installing CemStar were obtained from the

vendor for one kiln configuration (a wet kiln) at one facility. Data for other installations of

CemStar were not available for this report. The kiln capacity was 42 tons clinker/hour prior to

the installation of CemStar and 45 tons clinker/hour after the installation of CemStar. The

annualized cost for the conversion was calculated as $220,000. This annualized cost does not

include a credit for the increased production of clinker (approximately 3 tons/hour).

Uncontrolled emissions were calculated as approximately 1600 tons NOX/year. An average

emission reduction of 30% was determined for the installation of CemStar which results in 100

tons NOX/year. The cost effectiveness for this example facility was $550/ton of NOX reduced.

6.3.2 Low NOX Burner

The NOX reduction that may be achieved with a low NOX burner depends mainly on the

operating parameters. In fact, no guarantee on the NOX reduction level is usually provided by

burner vendors. With proper operation of the low NOX burner, 15 to 40 percent reduction in

NOX emissions should be possible.37 An average NOX reduction efficiency of 25 percent was

used in determining controlled NOX emissions and cost effectiveness of the low NOX burner

103

TABLE 6-13. CAPITAL COSTS FOR SCR PROCESS (1992 $)38

Model

no. Kiln type

Kiln capacity

(tons

clinker/hr)

Heat duty

(MM Btu/hr) PEC ($)

Freight and

sales tax ($)

Installation costs

direct and

indirect ($)

Contingency

costs ($)

Total capital

costs ($)

1 Wet 30 180 6,200 496,000 4,840,000 1,240 12,800

2 Wet 50 300 8,430 674,000 6,570,000 1,690 17,400

3 Long dry 25 113 4,790 383,000 3,740,000 958 9,870

4 Long dry 40 180 6,350 508,000 4,950,000 1,270 13,100

5 Preheater 40 152 5,820 466,000 4,540,000 1,160 12,000

6 Preheater 70 266 8,140 651,000 6,350,000 1,630 16,800

7 Precalciner 100 330 9,400 749,000 7,310,000 1,870 19,300

8 Precalciner 150 495 11,900 956,000 9,330,000 2,390 24,600

104

TABLE 6-14. ANNUALIZED COSTS FOR SCR(1992 $)38

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Operating

labor

($/year)

Ammonia

reagent

costs

($/year)

Maintenance

& overhead

costs ($/yr)

Energy

and fuel

costs

($/year)

Catalyst

costs

($/year)

Taxes

insurance

admin.

($/yr)

Capital

recovery

($/yr)

Total

annualized

costs ($/yr)

1 Wet 30 30,400 287,000 24,300 468,000 326,000 511,000 1,680,000 3,350

2 Wet 50 30,400 485,000 24,300 779,000 544,000 694,000 2,280,000 4,860

3 Long dry 25 30,400 218,000 24,300 304,000 212,000 395,000 1,300,000 2,510

4 Long dry 40 30,400 337,000 24,300 487,000 339,000 523,000 1,720,000 3,490

5 Preheater 40 30,400 238,000 24,300 421,000 293,000 480,000 1,580,000 3,090

6 Preheater 70 30,400 406,000 24,300 736,000 513,000 571,000 2,210,000 4,610

7 Precalciner 100 30,400 337,000 24,300 930,000 649,000 772,000 2,540,000 5,300

8 Precalciner 150 30,400 505,000 24,300 1,400,000 974,000 985,000 3,240,000 7,180

105

technology. For precalciner kilns, although only 60 percent of the heat duty was assumed to be

provided by the low NOX burners, all of the NOX emissions were assumed to result from these

burners. For existing direct-fired kiln systems, the costs involved in conversion of the firing

system increase the costs of NOX removal considerably. Table 6-15 presents the uncontrolled

and controlled NOX emissions for the eight model plants along with the cost effectiveness of low

NOX burner in an existing indirect-fired kiln. The cost effectiveness were within a close range for

the model plants and ranged from $300/ton of NOX for the large wet kiln to $620/ton of NOX for

the small long dry kiln.

Table 6-16 presents the cost effectiveness of low NOX burner installed in an existing

direct-fired kiln scenario. The cost effectiveness ranges from $760/ton to $1,200/ton of NOX

removed. The cost of firing system conversion doubled the cost effectiveness as compared to

those in Table 6-15. The conversion from direct fired to an indirect firing system is expected to

reduce the energy requirement per ton of clinker. The energy savings associated with the

increased efficiency and productivity are not considered in determining the cost effectiveness.

6.3.3 Mid-Kiln Firing of Tires

The cost effectiveness for the four model plants are given in Table 6-17 which range from

a credit of $460/ton to a cost of $730/ton of NOX removed. A NOX reduction efficiency of 40

percent was calculated for wet kilns and 30 percent for long dry kilns. This cost effectiveness

value includes a fuel credit for using waste-derived fuel and a tipping fee for the tires. If the tire

tipping fee is removed (but the fuel credit is retained - assuming waste material is free), the cost

effectiveness will range from $150/ton of NOX to $680/ton of NOX reduced.

6.3.4 Preheater/Precalciner Tire Derived Fuel

Costs for installing a tire derived fuel system at a precalciner kiln were obtained from one

facility. The purchased equipment and total capital investement costs were similar to the mid-

kiln firing costs (the majority of the cost is in the tire handling system). Cost effectiveness for

this kiln is based on the annualized costs of ($1,600,000/year), the emission reduction achieved

at that facility (emissions decreased approximately 30% from 3.4 lb/ton of clinker to 2.4 lb/ton of

clinker), a kiln capacity of 215 tons/hr, and an annual operation of 8,000 hr/yr. Cost

effectiveness is a credit of ($1,900/ton) for installing a tire derived fuel system on this kiln. This

cost effectiveness value includes a fuel credit for using waste-derived fuel and a tipping fee for

the tires. If the tire tipping fee is removed (but the fuel credit is retained - assuming waste

material is free), the cost effectiveness is calculated as a credit of ($480/ton) of NOX reduced.

106

TABLE 6-15. COST EFFECTIVENESS OF RETROFIT LOW-NOX BURNERS IN AN EXISTING INDIRECT-FIRED KILN(1997 $)

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat

duty

(MM

Btu/hr)

Uncontrolled

NOX

emissions

(tons/yr)

Controlled

NOX

emissions

(tons/yr)

NOX

removed

(tons/yr)

NOX

reduction

(%)

Total annualized

costs ($/yr)

Cost effectiveness

($/ton NOX

removed)

1 Wet 30 180 1,200 880 320 25 136,000 425

2 Wet 50 300 2,000 1,500 500 25 152,000 300

3 Long dry 25 113 860 650 210 25 130,000 620

4 Long dry 40 180 1,400 1,000 400 25 141,000 350

5 Preheater 40 152 940 700 240 25 140,000 580

6 Preheater 70 266 1,700 1,200 500 25 161,000 320

7 Precalciner 100 330 1,400 1,000 400 25 173,000 430

8 Precalciner 150 495 2,000 1,600 400 25 204,000 510

TABLE 6-16. COST EFFECTIVENESS OF RETROFIT LOW-NOX BURNERS IN AN EXISTING DIRECT-FIRED KILN (1997 $)

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat

duty

(MM

Btu/hr)

Uncontrolled

NOX

emissions

(tons/yr)

Controlled

NOX

emissions

(tons/yr)

NOX

removed

(tons/yr)

NOX

reduction

(%)

Total annualized

costs ($/yr)

Cost effectiveness

($/ton NOX

removed)

1 Wet 30 180 1,200 880 320 25 298,000 930

2 Wet 50 300 2,000 1,500 500 25 389,000 780

3 Long dry 25 113 860 650 210 25 241,000 1,100

4 Long dry 40 180 1,400 1,000 400 25 304,000 760

5 Preheater 40 152 940 700 240 25 282,000 1,200

6 Preheater 70 266 1,700 1,200 500 25 378,000 760

7 Precalciner 100 330 1,400 1,000 400 25 348,000 870

8 Precalciner 150 495 2,000 1,600 400 25 439,000 1,100

107

TABLE 6-17. COST EFFECTIVENESS OF MID-KILN FIRING

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat

duty

(MM

Btu/hr)

Uncontrolled

NOX

emissions

(tons/yr)

Controlled

NOX

emissions

(tons/yr)

NOX

removed

(tons/yr)

NOX

reduction

(%)

Total annualized

costs ($/yr)

Cost effectiveness

($/ton NOX

removed)

1 Wet 30 180 1,200 700 500 40 (14,600) (29)

2 Wet 50 300 2,000 1,200 800 40 (368,000) (460)

3 Long dry 25 113 860 600 260 30 189,000 730

4 Long dry 40 180 1,400 960 440 30 (9,300) (21)

108

6.3.5 Biosolids Injection

One facility in the United States is currently using biosolids injection technology on one

preheater/precalciner kiln. Cost effectiveness for this kiln is based on the annualized costs of

($320,000/year), the emission reduction achieved at that facility (emissions decreased from 2.4

lb/ton of clinker to 1.2 lb/ton of clinker), a kiln capacity of 215 tons/hr, and an annual operation

of 8,000 hr/yr. Cost effectiveness is a credit of ($310/ton) for installing biosolids injection on

this kiln.

6.3.6 Selective Noncatalytic Reduction

NOXOUT® is estimated to provide 40 percent NOX reduction based on the available test

data. Cost effectiveness for the two kilns described in section 6.2.3.2, using urea as the reagent,

is based on an uncontrolled emission rate of 3.8 lb NOX/ton of clinker, kiln capacities of 92 and

130 tons/hr respectively, annual operation of 8,000 hr/yr, and a NOX control efficiency of 40%.

Cost effectiveness is $1,000/ton for the smaller kiln and $2,500/ton for the larger kiln.

6.3.7 Selective Catalytic Reduction

The NOX reduction that may be achieved with SCR technology depends upon the reagent

stoichiometric ratio used, and the gas phase residence time in the SCR reactor. Although there

are no installations of the SCR technology in cement plants, 80 to 90 percent reduction in NOX

emissions has been achieved in SCR installations in other applications such as utility boilers and

gas turbines.39 The SCR equipment costs developed in Section 6.2.2.2 were based upon SCR

costs quoted for application on dry kiln exhaust gases with 80 percent design reduction in NOX

emissions. To determine the cost effectiveness of the SCR technology in cement kiln

applications, an 80 percent NOX reduction efficiency was therefore assumed and the results are

shown in Table 6-18. The cost effectiveness ranged from $3,140/ton to $4,870/ton of NOX

removed and are almost five to six times greater than the corresponding values for the ammonia-

based SNCR technology.

109

TABLE 6-18. COST EFFECTIVENESS OF SCR PROCESS38

Model

no. Kiln type

Kiln

capacity

(tons

clinker/hr)

Heat

duty

(MM

Btu/hr)

Uncontrolled

NOX

emissions

(tons/yr)

Controlled

NOX

emissions

(tons/yr)

NOX

removed

(tons/yr)

NOX

reduction

(%)

Total annualized

costs ($/yr)

Cost effectiveness

($/ton NOX

removed)

1 Wet 30 180 1,160 230 930 80 3,351,000 3,600

2 Wet 50 300 1,940 390 1,550 80 4,864,000 3,140

3 Long dry 25 113 860 170 690 80 2,506,000 3,630

4 Long dry 40 180 1,380 280 1,100 80 3,486,000 3,170

5 Preheater 40 152 940 190 750 80 3,087,000 4,120

6 Preheater 70 266 1,650 330 1,320 80 4,610,000 3,490

7 Precalciner 100 330 1,360 270 1,090 80 5,304,000 4,870

8 Precalciner 150 495 2,040 410 1,630 80 7,179,000 4,400

110

1. Vatavuk, W.M. Cost Estimating Methodology. In: OAQPS Control Cost Manual, Fifth

Edition, Vatavuk, W.M. (ed.). U.S. Environmental Protection Agency, Research Triangle

Park, NC. Publication No. EPA 450/3-90-006. January 1996.


Information Summary. Skokie, IL. December 31, 1998. 214 pp.

6.3.8 Summary of Cost Effectiveness

Table 6-19 summarizes the cost effectiveness for the various technologies. Table 6-19

also presents the ozone season cost effectiveness. The ozone season cost effectiveness is based

on the emission reduction that will be achieved in the 5 month ozone season (May-September).

TABLE 6-19. SUMMARY OF COST EFFECTIVENESS

(1997 $/ton NOX Reduced)

Technology Range of Annual

Cost Effectiveness

Average Annual

Cost Effectiveness

Average Ozone

Season Cost

Effectiveness

CemStar n/a 550 1,100

Low-NOX

Burners

Indirect-

Fired Kilns

300 to 620 440 1,060

Direct-Fired

Kilns

760 to 1200 940 2,260

Mid-Kiln Firing (460) to 730 55 130

Tire Derived Fuel at a

Precalcinera

(1,900)b (1,900)b (4,500)b

Biosolids Injection n/a (310)b (740)b

NOXOUT® 1,000 to 2,500 1,740 2,160

N/A - not applicable

( ) - indicates a negative costa The purchased equipment and total capital investment costs for a tire derived fuel installation

on a precalciner are very similar to mid-kiln firing.b Represents a single installation.

6.4 REFERENCES

111

3. Battye, R., and S. Edgerton, EC/R Incorporated, Chapel Hill, NC. Trip Report to

Mitsubishi Cement Corporation, Cushenbury Plant, Lucerne Valley, CA, December 2,

1999. Prepared for the U.S. EPA, RTP, NC, under contract No. 68-D-98-026, work

assignment No. 2-28. July 5, 2000.

4. Letter with attachments from Bramble, K.J., Cadence Environmental Energy Inc.,

Michigan City, IN, to W. Neuffer, U.S. EPA, RTP, NC. January 20, 2000. Cost of a

mid-kiln firing system.

5. Email from Joe Truini, Waste News to Lee-Greco, J., EC/R Incorporated, Durham, NC.

July 28, 2000. Average tire tipping fees.

6. Waste News - Current Commodity Pricing. Website:

(http://www.wastenews.com/current2.html). Accessed on January 21, 2000.

7. Cost of production downtime is based on clinker cost of $72.59 per short ton, 1997, from

the US Geological Survey Minerals Handbook and time loss of 2 days. Website:

(http://minerals.usgs.gov/minerals/pubs/commodity/cement/170398.pdf), January 1998.

8. Coal prices based on average price of coal delivered to other industrial plants by census

division and state, 1997, nominal dollars per short ton, from the U. S. DOE Energy

Information Administration. Website:

(http://www.eia.doe.gov/cneaf/coal/cia/html/t94p01p1.html), accessed on 5/22/2000.

9. Electricity prices based on U. S. Average Revenue per Kilowatt-hour by Sector and Class

of Ownership, from the U. S. Energy Information Administration/Electric Sales and

Revenue for 1997. Website: (http://www.eia.doe.gov/), accessed on 5/22/2000.

10. Natural gas prices based on Average Price of Natural Gas Delivered to U. S. Consumers

for 1997, from the U. S. DOE Energy Information Administration/Historical Natural Gas

Annual 1930 through 1997. Website: http://www.eia.doe.gov/), accessed on 5/22/2000.

11. Letter with attachments from Bramble, K.J., Cadence Environmental Energy Inc.,

Michigan City, IN, to W. Neuffer, U.S. EPA, RTP, NC. January 20, 2000. Cost of a

mid-kiln firing system.

12. Hourly wage rates are based on the Bureau of Labor Statistics website. Based on March

1997 dollars from Table 41. Website: (http://stats.bls.gov/ecthome.htm), accessed on

7/10/2000.

13. Letter and attachments from Willis, D.A., Blue Circle Cement, Inc., Atlanta, GA, to

Damle, A.S., Research Triangle Institute. June 4, 1993. Information on LINKman

Process Control System.

112

14. Battye, R., EC/R Incorporated, Chapel Hill, NC. Trip Report to Texas Industries (TXI)

Riverside Cement, Oro Grande facility, Oro Grande, CA, December 2, 1999. Prepared

for the U.S. EPA, RTP, NC, under contract No. 68-D-98-026, work assignment No. 2-28.

August 31, 2000.

15. Telecon. Neuffer, W., US EPA, Durham, NC and Mayes, G., TXI, Dallas, TX. March

24, 2000. Information on the CemStar Process.

16. Telecons. Lee-Greco, J., EC/R Incorporated, Durham, NC and Mayes, G., TXI, Dallas,

TX. July 20 and 28, 2000. Additional information on the costs of installing CemStar.

17. Electronic mail and telecon. Vaccaro, M., Pillard E.G.C.I., Marseille, France with Lee-

Greco, J., EC/R Incorporated, Durham, NC. July 26, 2000. Costs of low-NOX burners.

18. Letter from Denizeau, J., Lafarge Canada, Inc., Montreal, Quebec, Canada, to Crolius,

R.W., American Portland Cement Alliance, Washington, DC, August 24, 1993. Cost of

low NOX burners.

19. Letter and attachments from Bennett, J.H., California Portland Cement, Glendora, CA to

Neuffer, W.J., U.S. EPA, RTP, NC. July 2, 1999. Cost of firing system conversion.

20. PSM International, Inc. Available Control Techniques for NOX Emissions from the

Portland Cement Manufacturing Plant of California Portland Cement Company located

in Colton, California. Prepared by PSM International, Inc., Dallas, Texas for California

Portland Cement, Glendora, CA. March 6, 1995. Heat input for Colton Plant kilns. pg.

12.

21. Battye, R., EC/R Incorporated, Chapel Hill, NC. Trip Report to California Portland

Cement Company, Colton Plant, Colton, CA, December 2, 1999. Prepared for the U.S.

EPA, RTP, NC, under contract No. 68-D-98-026, work assignment No. 2-28. August 31,

2000.

22. Letter and attachments from Novak, L.S., RC Cement Co., Inc., Bethlemhem, PA, to

Crolius, R.W., American Portland Cement Alliance, Washington, DC, August 23, 1993.

Cost of firing system conversion.

23. Letter from Pap, E.S., Willis & Paul Group, Danville, NJ, to Stampf., Hercules Cement

Company, Stockerton, PA, April 6, 1988. Cost of firing system conversion.

24. Scrap Tire Recycling. Consumer Energy Information: EREC Reference Briefs. Website:

(http://www.eren.doe.gove/consumerinfo/rebriefs/ee9.html), accessed on 7/11/00.

25. Biggs, H.O. Biosolids Injection Technology: An Innovation in Cement Kiln NOX Control.

Mitsubishi Cement Corporation, Lucerne Valley, CA. Received on December 2, 1999

during plant trip.

113

26. Sun, W.H. NOXOUT® Process Demonstration on a Cement Kiln/Calciner - Ash Grove

Cement - Seattle Plant - Seattle Washington. October 28, 1993.

27. Letter and attachments Six, E.B., Spencer Fane britt & Browne LLP, Kansas City, MO to

P. Hamlin, Iowa Department of Natural Resources, Urbandale, IA. Lafarge Corporation

Draft Construction Permit for Air Emission Source Plant # 82-01-006, project # 96-494.

March 10, 1999. Attachment E - SNCR Data Analysis.

28. Lin, M.L., and M.J. Knenlein, Fuel Tech, Inc. Cement Kiln NOX Reduction Experience

Using the NOXOUT® Process. Proceedings of 2000 International Joint Power Generation

Conference, Miami Beach, FL., July 23-26, 2000.

29. Telecon. Lee-Greco, J., EC/R Incorporated, Durham, NC and Knenlein, M.J., Fuel Tech,

Inc. August 17, 2000. Additional cost information for NOXOUT® process.

30. Letter and attachments from Pickens, R.D., Nalco Fueltech, Santa Fe Springs, CA, to

Damle, A.S., Research Triangle Institute, October 15, 1992. Nalco Fueltech's urea-based

SNCR technology.

31. Letter and attachments from Wax, M.J., Institute of Clean Air Companies, Washington,

DC, to Damle A.S., Research Triangle Institute, December 7, 1992. Costs for application

of SNCR systems to cement kilns.

32. Letter from Seebach, M.V., Polysius Corporation, Atlanta, GA, to Willis, D., Blue Circle

Cement, Inc., Marietta, GA, June 18, 1993. Costs for Ammonia-based SNCR system.

33. Kupper, D., and L. Brentrup. SNCR Technology for NOX Reduction in the Cement

Industry. World Cement 23(3):4-9. March 1992.

34. PSM International, Inc., Dallas, TX and Penta Engineering Corporation, St. Louis, MO.

Review of Nalco Fuel Tech NOXOUT® program for Mid-Kiln Injection of urea to Reduce

NOX at the Coloton California Plant of California Portland Cement Company. Prepared

for California Portland Cement Company, Glendora, CA. October 26, 1994

35. Letter and attachments from Akita, A., Hitachi Zosen Corporation, Tokyo, Japan, to

Kohl, R.F., Arizona Portland Cement Company, August 2, 1991. Costs for an SCR unit

for Colton plant.

36. Letter and attachments from Bennett, J.H., California Portland Cement Company,

Glendora, CA, to Neuffer, W.J., U.S. EPA, RTP, NC. March 16, 1993. Costs for an

SCR unit for Colton plant.


U.S. EPA, RTP, NC. Derivation and data supporting development of cement plant NOX

emission rates. August 31, 2000.

114



NC. March 1994.

39. Smith, J.C., and M.J. Wax. Selective Catalytic Reduction (SCR) Controls to Abate NOX

Emissions. White Paper sent by Wax, M.J., Institute of Clean Air Companies.

September 1992.

United States Office of Air Quality Planning and Standards Publication No. EPA-457/R-00-002

Environmental Protection Air Quality Strategies and Standards Division September 2000

Agency Research Triangle Park, NC

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